214 CARBONIFEROUS LAMELLIBRANCHIATA. 



Neither description nor figures were given, and the first published diagnosis and 

 description was given by de Verneuil in his work on the ' Paleontologie de la 

 Russie,' who acknowledged that he had had the opportunity of perusing the MS. 

 of King's ' Monograph on the Permian Fossils,' in which volume a full and 

 detailed account of the genus was to appear. The generic name Schizodus must, 

 therefore, date from de Verneuil's work ; but as he himself distinctly states 

 that he has used King's MS. account, I have quoted the author as King in 

 de Verneuil. 



In a foot-note on p. 185 of his work King stated that he considered the 

 Sedfjwlchia glgantea of M'Coy to be a species of Schizodus; but I think he was 

 wrong in this case. He also stated that a large number of shells classed under 

 six different genera by M'Coy were referable to his new genus ; these, however, I 

 now refer to Protoschizodus. 



Sowerby included under his genus Axinus two very different shells, — A. 

 angulatus from the London Clay, and A. obscurus from the Permian; the former 

 had an edentulous hinge, and the latter was shown by King to possess well- 

 marked hinge-teeth, so that there was little or no doubt of the wisdom of erecting 

 a new genus for shells possessing the latter characters ; Axinus being now classed 

 in the family Ungulinidae, Schizodus in the Trigonidse. 



Professor King described the hinge of Schizodus as consisting of two smooth 

 cardinal teeth in the right valve, with three in the left, those of the latter being- 

 placed in front of those in the right valve. With this description I am not able 

 entirely to agree, for I find in the best preserved and full-grown specimens that 

 there are three distinct teeth in each valve, only one of which, however, is really a 

 cardinal tooth, the anterior and posterior teeth in each valve being lateral teeth; 

 and that, in direct opposition to King's statement, the teeth of the right valve are 

 always in front of those in the left. This misstatement is fully accounted for by 

 the non-discovery of the anterior tooth of the right valve, for in every other detail 

 the figures of the hinges given in the ' Monograph of Permian Fossils,' pi. xv, 

 fig. 29, are very fairly accurate. 



The anterior tooth in the right valve is sessile, and the least apparent of any, 

 being only a thickening of the edge of the hinge-plate (PI. XVI, fig. 2), but the 

 cardinal tooth of the left valve is the larger, and is comparatively thick, and there 

 is not room enough to receive it in the small hollow between the anterior and 

 cardinal teeth of the right valve ; and these two teeth are connected in the right 

 valve by a plate of shell, while the tooth-cavity posterior to the cardinal tooth is 

 large and perfectly free. These details are well shown in a right valve of 

 8. Pentlandicus, from Woodhall, Water of Leith (fig. 2, PI. XVI), and a left valve of 

 8. Harii, Miller, from the Upper Coal-measures of Kansas (fig. 1 a, PI. XVI), which 



