Monday, 20th May 1878.

DAVID STEVENSON, Esq., C.E., Vice-President,
in the Chair.

The following Communications were read :

1. On the Genus Rhizodus. By Dr R. H. Traquair.

(Abstract.)

In this paper the author first sketches the history of Rhizodus, from its discovery by Ure of Rutherglen to the most recent papers on the subject.

Placed by Agassiz among the "Coelacanthi" (i.e., cycliferous Crossopterygia of modern nomenclature) it was classified by Professor Huxley in the cycliferous division of his family Glyptodipterini, along with Holoptychius, Glyptolepis, Dendrodus. The discovery by the author, in 1875, of its subacutely lobate pectoral fin revealed the fact that it was much more closely allied to Rhizodopsis than to Holoptychius, and that it ought, along with the former genus, to be classed in a family (Cyclodipterini) distinct from the acutely lobate Holoptychiidae. The author does not consider the identity of Leidy's genus Apepodus with Rhizodus as proved.

M'Coy admitted two species of Rhizodus-R. Hibberti, Agassiz, and R. gracilis, M'Coy, merging with the former of these the Holoptychius Portlockii of Agassiz. An examination of the types of Holoptychius Portlockii, preserved in the Museum of Practical Geology, shows, however, that this species is not only specifically but also generically distinct from Rhizodus Hibberti, as the teeth are devoid of the cutting edges characteristic of Rhizodus, and in this particular, as well as in the minute striation of the surface, they closely resemble those of Hancock and Atthey's genus Archichthys, to which the author proposes to transfer it, at least provisionally.

An investigation of the large store of Rhizodus remains from the Gilmerton ironstone, belonging to the Edinburgh Museum of Science and Art, shows the presence of two well-marked species of Rhizodus, differing in the bulk to which they attained respectively, as well as in the relative thickness of the scales, the shape of many of the

bones, and the external sculpture as well of the bones as of the scales. For the larger of these two species, there can be no doubt of the propriety of retaining the specific name Hibberti, as it is clear that its enormous laniary teeth, as occurring in the limestone of Burdiehouse, and at first considered by Hibbert to be reptilian, originally suggested the name Megalichthys Hibberti to Agassiz, which he afterwards altered to Holoptychius Hibberti, after eliminating the Saurodipterine remains previously confounded with them, and to which latter he then limited the term Megalichthys, rather unfortunately, as "Megalichthys" is the smaller fish! M'Coy's R. gracilis is certainly a synonym of R. Hibberti, the apparent greater slenderness of the dentary bone being due to the infradentary plates (not known to M'Coy) being, as is often the case, awanting in the specimen; and as regards the greater slenderness of the anterior laniary, a large series of teeth from Gilmerton shows every possible amount of gradation in that respect. For the smaller species, whose remains have hitherto been confounded with R. Hibberti, the author proposes the name of R. ornatus.

1. Rhizodus Hibberti, Ag. sp.

This species must have attained a gigantic size, a detached dentary bone in the Edinburgh Museum measuring no less than 25 inches in length. Externally the cranial bones are ornamented by a rather fine tuberculation, the tubercles more or less confluent with tortuous ridges. The mandible displays the same structure as in Rhizodopsis, the dentary element being narrow, pointed behind, thick in front, where it carries the anterior or symphyseal laniary tooth, the three other laniaries behind being borne upon separate internal dentary pieces. Below the dentary, and forming the lower margin of the jaw, are three infra-dentary plates, while posteriorly the articular region is covered by a large plate representing the angular element. Other determinable bones described in this paper are the maxilla, which, as in Rhizodopsis, only bears small teeth, the principal jugular, the operculum, the clavicle, the infra-claricular; there are others also whose place in the skeleton is not easily determinable. The clavicle and infra-clavicular are not tuberculated like the cranial bones, but ornamented with delicate reticulating ridges and pits; the posterior superior angle of the infra-clavicular

is produced upwards and backwards in a long slender process. The scales are comparatively thin and very large, sometimes, as noticed by Hibbert, attaining a diameter of 5 inches; usually they occur in a broken condition. Their attached surface is marked by a central boss and concentric lines of growth. The outer surface, very rarely seen, is ornamented by closely set granules, which towards the posterior border of the exposed area are confluent into wavy ridges terminating in the margin. These seem certainly to be the scales attributed to R. Hibberti by M'Coy, but not by Young; they are probably also the same as the undescribed 'Phyllolepsis tenuissimus' of Agassiz.

R. Hibberti occurs throughout the Cementstone and Carboniferous Limestone series of Scotland, the most noted locality being Gilmerton, near Edinburgh.

2. R. ornatus, sp. nov. Traquair.

To this species, which seems never to have attained anything like the dimensions of R. Hibberti, belong the specimen showing the pectoral fin described by the author in 1875, the head described by Mr L. C. Miall, and in fact nearly all the specimens in which any portion of a fish with bones or scales in situ is shown. The ornament of the cranial bones is somewhat similar in character to that in R. Hibberti, but very much coarser; the same is the case with the bones of the shoulder. Of the bones the following have been recognised by the author-dentary, operculum, principal jugular, clavicle, infra-clavicular; there are also others whose determination is still somewhat doubtful. The clavicle differs somewhat in form from that of R. Hibberti, its lower portion being narrower from before backwards. The expanded portion of the infra-clavicular is also shorter than in the larger species, but the same slender process is sent backwards and upwards from its posterior superior angle. The pectoral fin is subacutely lobate. The scales are thicker than those of R. Hibberti. The exposed area of the external surface is marked with short, interrupted, wavy, reticulating ridges, whose direction is mainly parallel with the posterior border of the scale; in the interval between these, more delicate ridges are seen radiating from the centre. It is apparently on a scale of this species that Dr Young has founded his description of those of R. Hibberti.

R. ornatus occurs in the Calciferous Sandstone series of Scotland, as at Burdiehouse in Mid-Lothian, and Pittenweem in Fifeshire; but it is especially abundant in the black band ironstone of the Lower Carboniferous Limestone group at Gilmerton, above which horizon it has not yet been discovered.

2. On the Anatomy of a recent species of Polyodon, the Polyodon gladius (Martens), taken from the river Yangtsze-Kiang, 450 miles above Woosung. Part III., being its Viscera of Organic Life. By P. D. Handyside, M.D.

The author proceeded with his anatomical description of the respiratory, circulatory, and pneumatic systems in this remarkable fish; referring to the differences that exist in the male, the female, the young, and the adult specimens. He also shortly noticed the alimentary and other viscera of Organic life.

Dr Handyside illustrated his paper by 24 additional drawings -including 7 microscopic views of structure in this fish.

The fourth and last part of Dr Handyside's paper will consist of a description of the articular system and the endo-skeleton of the Polyodon gladius.

3. A Mechanical Illustration of the Vibrations of a Triad of Columnar Vortices. By Sir William Thomson.

4. Fourth Report of Boulder Committee, with Remarks. By D. Milne Home, Esq.

Since the last Report was drawn out and laid before the Society, the Convener has had an opportunity of inspecting a considerable number of boulders not mentioned in previous Reports. Some of these are interesting, on account not only of size, but also of shape, marks on them, and position. The Committee consider that advantage will result from a special description of these, and from woodcuts of a few.

The cases have been arranged, as in previous Reports, according to counties, to indicate the geographical position of the boulders, and enable persons desirous of inspecting them, to know where to find them.