340 CARBONIFEROUS LAMELLIBRANCHIATA. 



species of this genus are related to Myophoria. Kayser (' Jahresbuch Preuss. Geol. 

 Laudes,' 1844) tkougkt tkat tkere was more similarity between Mccynodon and 

 Mytilomorpha, but Avitk this Freeh evidently does not agree. Beuskausen (op. supra 

 clt.) retains botk Goniophora and Mecynodon, and he gives suck fine figures of 

 the kinge-plate of the latter genus as make it at once plain that the two genera 

 Lave little or nothing in common. The shape and external marking of the valves 

 in Mytilomorpha, and the possession of traces of a byssal sinus, seem to point 

 conclusively to a descent from a mytiliform ancestor ; but at the same time tke 

 position of the adductor muscle-scars, tke large lunule and escutcheon, and tke 

 structure of tke kinge and absence of an internal ligament, skow tkat tke skell 

 cannot be retained in any genus of tke family Mytilidse. I kave not been able to 

 satisfy myself tkat a byssus was actually present, tke inferior margin of the 

 valves of Mytilomorpha containing no byssal notck. The genus is, on the other 

 hand, closely related to Gypricardella and Sanguinolites, in tke latter of wkick 

 M. rhombea kas been placed by de Koninck. I tkink, kowever, tkat, seeing kow in 

 Devonian times many allied forms were in existence, it is better to separate tke 

 strongly keeled mytiloid group from Sanguinolites, as other autkors kave done. 

 Cypricardella kas such a ckaracteristic kinge and concentric markings on tke 

 surface tkat tkere can be no doubt of tke propriety of distinguisking these two 

 genera. Sanguinolites may be distinguished from Mytilomorpha by its more 

 transverse, less oblique, less strongly carinate form, with the surface of the valves 

 more ornate, generally furnished with lamella? or concentric sulcations and ridges, 

 having a rolled hinge-plate, and one or more radiating folds on the dorsal slope. 



Although much more numerous a species in Devonian times, I only refer two 

 species of Carboniferous Lamellibrancks to Mytilomorpha, one of wkick is new. 

 The typical Carboniferous form is that described by Phillips as Cypricardia 

 rhombea. 



De Ryckholt referred the same species to Solenopsis. 



It seems probable, from the description, that the shell described by Waagen 

 (op. supra cit.) as Eucharis grandseva, from the Salt Range of India, should rather 

 be referred to Mytilomorpha. I am at a loss to conceive why he should have 

 thought that there existed grounds for referring this shell to any genus of the 

 Myidm. His description is an excellent one, and perfectly characteristic of the 

 genus Mytilomorpha. 



Mytilomorpha rhombea, Phillips, sp., 1836. Plate XXXVIII, figs. 6 — 11. 



Cypkicaedia hhombea, Phillips, 183G. Geo], Yorks., pt. 2, p. 209, pi. v, fig. 10. 

 — glabeata, Phillips, 1836. Ibid., p. 209, pi. v, fig. 25. 



