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



Agassiz's systematic catalogue and in his descriptions, must, 

 according to the rules usually followed, be considered as tlie type of 

 the genus.^ It is to be hoped that more satisfactory information as to 

 the real characters and affinities of that form may soon be forth- 

 coming. Meanwhile it would seem that the teeth known as Lopliodus 

 are in fact those situated in the anterior part of the mouth of genera 

 more or less allied to CocliUodtis. For although Professor Owen, in 

 his paper •' On the Teeth of Cochliodonts," held that there is "no 

 ground for assuming that the symphyses were prolonged, as in 

 Cestracion, for the support of conical or any other teeth," ^ Messrs. 

 Newberry and Worthen have, as is well known, described a species 

 of Cochliodus (C. nohilis) from the Carboniferous Limestone of 

 Illinois, in which, with the Cochliodont plates, were associated teeth 

 of decidedly Lophodont configuration (Helodus nohilis, N. & W.) in 

 such a way as to lead to the belief that these " occupied the central 

 portion of the jaw in two or more rows between the large convoluted 

 teeth which we have described under the name of Cochliodus nohilis." 

 And regarding the very species of Lopliodus occurring on our present 

 specimen, these authors remark on a previous page : — " The median 

 teeth of Cochliodus, a group which must include several described 

 species of Helodus (e.g. H. Icevissimus, H. didymus, H. turgidus, etc.), 

 have been found in regularly diminishing series like some of those 

 now figured." ^ It is now shown that two of those (viz. Icevissimus 

 and didymus) occupied a position in the front of the mouth of 

 Psephodus, which, although not Cochliodus, has certain obvious 

 points of affinity with it. Psephodus is still included in the Cochlio- 

 dontidse by Messrs. St. John and Worthen.* 



EXPLANATION OF PLATE VIII.5 



EiG. 1. Anterior part of the specimen of Psephodus magnus described in the text, 

 showing what remains of the teeth and cartilage of the jaws. 



{a) Tooth supposed to be the " middle" tooth of Psephodus magnus 



by M'Coy and Davis, seen from its attached surface. 

 {b) Portion of tooth supposed by these authors to be the " posterior " 



tooth. 

 {g) Teeth referable to Helodus or Lophodus Icevissimus. 

 ,, 2. Portion of the same specimen split off and turned up, showing additional 

 teeth. 

 {b) Tooth whose broken margin is shown at b in the previous figure. 



(c) Tooth of type of Helodus rudis, M'Coy. 



(d) Helodus planus. 



\e) Helodont teeth of peculiar form. . 

 (/) Helodus or Lophodus didymus. 

 {g) Helodus or Lophodus Icevissimus. 

 ,, 3. Tooth a in Fig. 1, seen from its convex surface, 

 ,, 4. Tooth b in Figs. 1 and 2, seen from its convex surface. 



1 Note added July 20th. A recent examination of the specimens of Helodus 

 simplex in the British Museum has convinced me that these teeth are truly 

 "Lophodont" in form, and consequently the genus Lophodus must be altogether 

 abolished. 



2 Geol. Mag. Vol. IV. 1867, pp. 59-63. 



^ Geol. Survey of Illinois, vol. ii. Palaeontology, p. 74. 

 * Geol. Survey of Illinois, vol. vii. Palseontology. 



5 [This Plate is by permission of the Council of the Geol. Soc. of Glasgow allowed 

 to appear in the Geological Magazine.] 



