102 REPORT— 1869. 



and dimensions of the orbital cavities, as well as in the dimensions of the occipital 

 comua. Measurements of two crania in inches : — length 12 and 13, breadth 6'5 and 

 9-5 ; breadth between cornua 2-87 and 2-75. The characters do not in the mean- 

 time justify the establishment of a new genus for these crania. 



Megalichthys. The following species were defined from specimens in Mr. Thom- 

 son's cabinet, obtained from the Lanarkshire coal-field : — 



31. Hibherti. Scale covered with tine-grained, smooth, glossy enamel. In this 

 species occurs most frequently that imperfect development of ganoin referred to 

 in Q. J. Geol. Soc. 1866, pp. 6()7-8. 



M. coccolepis, n. sp. Scale usually of a rich brown colour, set with stellar 

 tubercles, recalling the " berry-bone " of the Old Red Sandstone. 



M. ruffosvs, n. sp. A less frequent form ; the scale is usually pale, not enamelled, 

 covered with asperities more or less confluent, never stellar. "With this scale is 

 associated a tooth which Dr. Young described as diagnostic of I'homhoptychius 

 (Q. J. Geol. Soc. 1866; p. 606), but which turns out to be common to two -distinct 

 genera. 



On Teeth and Dermal Structure associated with Ctenacanthus. 

 By James Thomson, F.G.S. 



The author stated that he had discovered in the spring of this year, in the 

 neighbourhood of Airdrie, Lanarkshire, a slab of ironstone measuring 30x14- 

 inches ; although only a fragment, yet it exhibits, 1st, a mass of shagreen ; 2nd, two 

 spines of Ctenacanthus major ; 3rd, a nimiber of teeth, Chuhchis mirabilis, Agassiz, 

 evidently in their proper relative position, the slightly curved line in which they 

 are disposed suggesting the contour of the mouth, and Ipng at a higher level than 

 those which were exposed ; 4th, a fragment of a small spine, the cross section of 

 which gives as its outline a spherical triangle with the posterior side less than the 

 others ; the anterior face is round and smooth, while the posterior face is flat. Along 

 the margins of the posterior face there are two rows of pointed tubercles curving in- 

 wards and downwards. Being thus formed on the upper surface of the head, it is 

 natural to infer that it was situated on the occipital region of the fish. This in- 

 ference is supported by subsequently finding another spine imbedded in another 

 slab, which, like the former, is associated with the teeth of Cladudus mirahilis. 



On removing the ironstone from the underside of the slab immediately over the 

 mouth, the author laid bare the skin, and found imbedded on its surface numerous 

 minute bodies, consisting of two, three, and four curved diverging points rising from 

 an expanded base, from which a sharp keel on the convex side passed to the apex of 

 each. 



On other parts of the slab are found similar bodies, larger than those found on the 

 crown of the head, but possessing similar tooth-like characters, divided into two, 

 three, four, and in a few instances into six divergent points, and keeled along the 

 convex or dorsal side ; and on a slab which Dr. Eankin Carluke allowed tlie author 

 to examine, were found a mass of similar teeth-like bodies, which exhibited similar 

 characters, in one instance divided into fifteen divergent points, and also associated 

 with the teeth of Cladodus. 



In another slab, found at the same place and at the same time, were im- 

 bedded in a patch of shagi-een the so-called teeth of Diphdus c/ihhosm, very nu- 

 merous, and crowded together without order. "VVe have associated with these 

 another form of teeth-like tubercles, smooth, enamelled and circular in section ; 

 they are relatively larger, while the recui-ved apex is more pointed than the tu- 

 bercles before described ; they are occasionally found in patches of greater numbers ; 

 in some instances in clusters of eight and nine, and are attached to broad flat bases. 

 Finding such an amount of co-related evidence, the author prepared microscopic 

 sections of patches which were detached from the mass. After doing so, he was led to 

 refer to the results of other investigators, and found that Professor Owen had got 

 forwarded to him from Mr. Craggs similai' forms found in the Newcastle coal-field, 

 and which he described in a paper read to and published by the Odontological So- 

 ciety. He describes them as teeth, some of which he names Ditodus diverffens, 

 Mitrodus quadricormis, Ochhdus crassus, Gastrodus ^trepositus. 



