MYTILOMORPHA. 339 



left valve has a strong fold or tooth in front, which is received into a corre- 

 sponding cavity in the right valve. Pallial line entire, remote from the margin. 



Exterior. — The surface is ornamented with close, fine, concentric lines of 

 growth, often subimbricate. 



Observations. — The name Goniophora was proposed by Phillips (op. supra cit.) 

 for the Gypricardia cymbceformis of Murchison (' Sil. Syst.,' pi. iii, fig. 10 a), but 

 no definition of the genus was given. Hall was the first to give a regular 

 description of the genus, which he adopted for a number of shells occurring in the 

 Devonian series of the State of New York. It appears that the term Goniophorus 

 was invented by Agassiz for a genus of Crinoids, and it must therefore be 

 regarded as preoccupied and inadmissible for a genus of shells. None of the 

 synonyms of the genus can be retained, as they all were founded on shells possess- 

 ing characters distinct from the genus under discussion, and it is therefore 

 necessary to erect a new genus. The term Mytilomorpha seems to me to be a 

 suitable one, more especially as I think there is strong evidence that this genus is 

 descended from a mytiliform ancestor. Hall's description of the hinge of Gonio- 

 phora is as follows : " Hinge furnished with a strong oblique fold or tooth in the 

 left valve, situated just beneath the beak, and a corresponding depression in the 

 right valve. No lateral teeth have been observed." These characters obtain in 

 the Carboniferous species. There is certainly no lateral tooth, and I have seen 

 traces of the anterior teeth, but unfortunately I have no specimen sufficiently 

 perfect to figure which shows them. 



Whidborne, Neumayer, S. A. Miller, and Beushausen all adopt the genus 

 Goniophora for Devonian shells, and the latter gives a lengthy description of the 

 genus, following Hall in his account of the hinge. Whidborne describes his shell 

 as possessing " one if not two small oblique teeth on each valve below the umbo, 

 and perhaps a long transverse lateral tooth behind." M'Coy states (' Brit. Pal. 

 Foss.,' p. 275) that the shell on which Phillips founded the genus does possess a 

 " moderately slender lateral tooth," but referred the shell to Orthonotus, Conrad. 

 There can be no doubt as to the intimate external resemblance of the Carbo- 

 niferous shells which I have placed under the genus Goniophora, to those 

 described by the above authors from the Devonian beds of Germany and North 

 America. Neither can there be any doubt as to the advisability of removing these 

 species from the genus Gypricardia on account of the structural differences in the 

 hinge, and, moreover, according to Fischer (' Manuel de Conchyliologie,' p. 1072), 

 Gypricardia, Lamarck, 1819, was forestalled by Libitina, Schumacher, 1817. 

 Neumayer, however, erected a new family, Goniophorinse. It would seem that 

 some of the species included under Mecynodon, Kef erst, have some external 

 resemblance to Mytilomorpha.. Some species are, however, entirely without the 

 typical carination. Freeh (' Zeit. deutsch. Geol. Ges.,' Bd. xli, p. 127) thinks some 



