Dr. Traquair — On Psephodus magnus,from E. Kilbride. 341 



which again the surface is mainly covered by calcified cartilage, 

 through which (at h) the broken margin of another large tooth may 

 be seen projecting. A fracture enables us to raise this cartilaginous 

 portion of the specimen, bringing into view upon its under surface 

 (Fig. 2) a large number of additional teeth, among which is the large 

 one whose broken edge I have already alluded to. This is firmly 

 fixed to a stout long-shaped piece of cartilage, resembling a jaw 

 ramus, which is not, however, preserved in its entirety, being 

 obliquely broken off in front. The tooth itself (Fig. 4) belongs to 

 the category reckoned by M'Coy and Davis as the " posterior " tooth 

 of Psephodus magnus, and of this it represents one of the rude 

 convex varieties. The margin regarded by M'Coy as "inner" is 

 broken away ; the anterior and posterior margins are crenulated ; 

 the so-called " outer " bent margin is entire and smooth. 



These two teeth, above described, are the only large ones seen in 

 the specimen. They undoubtedly belong to Psephodus magnus, 

 Agassiz, and not to Tomodus convexus, as stated by Mr. Coutts ; but 

 his mistake is readily excusable when we consider the difficulty and, 

 in many cases, impossibility, of identifying Agassiz's MS. genera, 

 until the appearance of Mr. Davis's work. 



There are no less than forty-four smaller teeth exhibited in the 

 specimen. Mr. Coutts mentions thirty-two, including the two large 

 ones ; but by careful working out I have been able to uncover the 

 additional number. They are mostly rather confused in position; 

 but as seen in Fig. 2, several groups occur of two, three, and four in 

 apposition. The most posterior of these smaller teeth (c) is isolated 

 from the rest, and somewhat resembles Helodus rudis of M'Coy, 

 though smaller in size. It is oval in shape, i inch in length by 

 i in breadth, slightly convex on the surface, and with its margin 

 sloping and crenulated. 



More than twelve of the teeth {d) in front of this and lying 

 between the two larger ones are clearly identifiable with Helodus 

 planus, though they exhibit considerable variety in size as well as 

 shape ; the largest being nearly one inch, the smallest f inch in 

 length. Some of them are much broader behind than in front, with 

 oblique posterior margins, others are more rectangular ; some exhibit 

 considerable lateral convexity of the crown, on others the surface is 

 more flattened ; in all, the margins are crenulated. 



Closely behind the large tooth (6) may be observed four teeth of 

 a peculiar form (e), three of them being in apposition. The largest 

 of these is --^ inch in length by \ in breadth ; the shape somewhat 

 rectangular, but from the middle of one margin a small angular 

 point projects over the tooth next in advance. The margins are 

 crenulated. 



The remaining teeth are placed in advance of those already 

 described, and most of them, where their shape is clearly exhibited, 

 present the characters of Eomanowski's genus Lophodus, — a genus 

 instituted for those Helodont teeth which possess a well-marked, 

 more or less compressed, and vertically striated or crenulated root.^ 

 1 Bull. Soc. Imp. Nat. Moscow, vol, xxxvii. 1864, pp. 157-170, 



