SCHIZODUS. 215 



I figure here as it is a large shell, and consequently possesses all the details of 

 the hinge on a large scale ; the formula being ^ °loioi f rom before backwards. 



Waagen says (op. sup. cit), p. 232, " In the right valve the posterior cardinal 

 tooth is generally very small and firmly adpressed to the hinge margin, superseded 

 by a not long but very distinct fulcrum. Anteriorly the hinge margin is some- 

 what thickened, forming an indistinct third anterior cardinal tooth." In the left 

 valve he describes the three teeth, but states that the cardinal tooth is not always 

 bifid. 



De Verneuil (op. supra cit.) described only two hinge-teeth in each valve — an 

 error which King pointed out. 



De Ryckholt (' Melanges paleontologiques,' partie ii, p. 79) places Schizodus 

 as a synonym of Dolabra, M'Coy, the hinge of which genus as described by M'Coy 

 consists of " two long diverging cardinal teeth, and two lengthened posterior 

 lateral teeth." M'Coy was of opinion that Schizodus of King was identical with 

 Myophoria, Bronn, from the Muschelkalk, and there is no doubt that the two 

 genera are closely allied. In Myophoria, however, the cardinal teeth are striated, 

 and the anterior adductor muscle is situated upon an elevated prominence, and 

 the surface is ornamented with radiating ribs — characters absent in Schizodus. 

 King, however, seems to have been quite aware of the close similarity of these 

 two genera. 



The affinities of the genus Mijophoria have been discussed by Neumayer, Freeh, 

 and others. Their views are discussed in detail by S. Frh. v. Wohrman in vol. xliii, 

 1893, of the ' Jahrbuch der k.k. Greol. Reichsanstalt.' He describes the hinge 

 of the left valve of Myophoria as having three teeth; the posterior, commonly 

 long and short, may become short and blunt, and almost entirely disappear in 

 the posterior edge of the valve. The cardinal tooth strongly, slightly, or not at all 

 bifid on its articular surface ; and the anterior tooth formed by a narrow thickening 

 of the hinge-plate, which may become strongly developed, and in front of which is 

 a tooth-socket. The hinge of the right valve possesses as a rule two teeth, the 

 posterior, either long and narrow or short and thick ; the cardinal tooth always 

 rises below the umbo, and is directed forwards : there is also at times an anterior 

 tooth on the anterior edge, well marked in M. truueata, Groldfuss. 



It is at once evident that the hinge as here described is identical with those 

 which I figure (PI. XVI, figs. 1 and 2) as Schizodus Harii and 8. Pentlandicus. 

 When discussing the affinities of Schizodus, v. Wohrman remarks on the difficulty 

 of distinguishing this genus from Myophoria. He says the tooth formula may be 

 the same in both, but the chief difference in Schizodus is its possession of a deeply 

 bifid Trigonia-like tooth in the left valve. Waagen ('Pal. Indica,' ser. 13, vol. i, 

 " Salt Range Fossils ") appears to have considered that the absence of the muscle 

 ridge, the greater distance of the muscle from the hinge, and the opisthogyrous 



