PROTOSCHIZODUS. 227 



the hinge; and because of this fact, as early as 1873, he had published his views 

 with a descriptive account (pp. ctt.) under the name Niobe ; but, finding that the 

 name had been proposed by Gerard for a genus of Gasteropoda, he eventually 

 adopted the name Pvotoschizodus. In assuming that King was wrong in 

 referring certain Carboniferous species to Schizodus de Koninck also fell into 

 error ; for certain Carboniferous species undoubtedly belong to this genus, e. g. 

 S. axiniformis, Phillips, sp., S. cavbonarius, Sowerby, sp., and S. Pentlandicus, 

 Rhind, sp. The shells described as Amphidesma by Portlock have been referred 

 to Schizodus by the authors of catalogues previous to de Koninck' s discovery of 

 the hinge characters, and erroneously placed with others typical of that genus, 

 but I cannot find that these species were ever included by King in the genus 

 Schizodus. 



De Koninck describes eleven species of Pvotoschizodus, nine of which are said 

 to be new ; but one of these had been referred by de Ryckholt to another genus. 

 Three of these species are founded on single specimens, and five others are stated 

 to be very rare. It is probable that the species named P. Halli, P. impvessus, 

 and P. uucinatus are really one and the same, although they exhibit some slight 

 variation in the degree of truncation and obliquity of the posterior end ; but I 

 think that much of the variation of contour seen in the Belgian specimens is due 

 to incomplete filling of the cast of the shell during fossilisation and similar causes. 



Tornquist (op. cit.), following Freech, thinks that Pvotoschizodus has no real 

 relation to Tvigonia, and that the genus is more closely connected with Scaldia, 

 the edentulous Edmondidse, and Cavdiomorphsc, and belongs to the family 

 Astartidse. I am unable, however, to agree with him, and consider that de 

 Koninck was more correct in assuming a close family relationship to Schizodus 

 (as the name indicates) upon the other characters of the interior. 



There is no doubt that many of the species included under the genus Dolabra 

 by M'Coy belong to Pvotoschizodus, and that M'Coy's generic name would have 

 been retained had he not selected the Devonian Cucidlsea of Marwood as the type 

 of his new genus, and to which unfortunately his description does not correctly 

 apply. On the other hand, the diagnosis of Dolabva differs very widely from that 

 of Protoschizodus, it being stated that the shells are " slightly inequivalve," and 

 that the hinge consists of " two long diverging cardinal teeth, anterior one 

 longest, and two lengthened posterior lateral teeth." 



In a later diagnosis of the genus (' British Palasozoic Fossils,' p. 269) there is 

 a considerable difference from that originally given ; for example, the hinge is 

 stated to have " one thick, elongate, posterior lateral tooth in each valve, 

 inclining at an acute angle from the hinge-line, that of the left valve sometimes 

 bifid ; " and the genus is placed in the family Mijtilidse. None of the shells which 

 I now refer to Pvotoschizodus are inequivalve or have any Mytiliform characters. 



