ANIMALS. 167 



two to five, according to species), as in Perna and Gervillia ; and it possesses anterior 

 and posterior linear teeth/ similar to those of the Cucullsea-toothed Arks."^ 



Until more is known of the general characters and chronogeny of a number of 

 palaeozoic fossils apparently belonging to Pterinea, Goldfass, Actinodonta, Phillips, 

 Modiolopsis, Hall, Myalina, Koninck, and some undescribed genera, it is impossible to 

 speak with any safety as to the afl&nities of the present genus, or even the family which 

 it typifies. " Bakevellia appears to be related to Pterinea; but the latter has no 

 cartilage-pits :" its resemblance to Avicula is purely simulatory. 



Bakevellia ceratophaga, Schhtheim. Plate XIV, figs. 24, 25, 26, 27. 



Mytilites keeatophagus, Schl. Akad. Miinch., vol. vi, p. 30, pi. v, fig. 2 a, b, c, 1816. 



— CERATOPHAGUS, „ Pctrcfactenkunde, p. 293, 1820. 



— — „ Boue, Edin. Phil. Journ., vol. xii, p. 144, 1825. 

 Avictjla — striated sp., -which resembles a Gervillia, J. de C. Sow. Trans. Geol. Soc. 



Lend,, 2d series, vol. iii, p. 119, 1829. 

 Mytilus keratophagus, Schl. De la Beche, Geol. Man., Germ. TransL, p. 459, 1832 ; 



3dEng. Ed., p. 573, 1833. 

 — ? — „ Phillips, Encyc. Met., vol. iv, p. 617, 1834. 



Goldfuss, Petrefacta, 2d part, p. 126, pi. 116, fig. 6. 



Geinitz, Gsea von Sachsen, p. 96, 1843. 



De Verneuil, Bull. Soc. Geol. de France, 2"° serie, t. i, 



p. 33, 1844. 

 Geol. Russ., vol. i, p. 224, 1845. 

 Geinitz, Grundriss, p. 457, 1846. 

 Tennant, Strat. List, p. 88, 1847. 

 King, Catalogue, p. 10, 1848. 

 Howse, Trans. T. N. F. C, vol. i, p. 249, 1848. 

 Geinitz, Versteinerungen, p. 10, pi. iv, figs. 16, 17, 1848. 



Avicula ceratophaga 

 keratophaga 



Bakevellia ceratophaga 

 Avicula keratophaga 

 Gervillia — 



Diagnosis. — " Shell subrhomboidal, arched, the front wing rounded, the one behind 

 falciform produced, with regular concentric lines."^ 



Bakevellia ceratophaga is so truly like an Aviada, in its long hinge-line, slight 

 umbonal divarication, prominent incremental lines, long posterior wing, anterior lobe, 

 and byssal or ^edal sinus, that Schlotheim, who published some excellent figures of it, 

 was struck with its " resemblance to young specimens of Mytilus Jtirundo, Linn."* 



It is somewhat variable in form ; but its distinctive characters are easily recognised 

 in the line of separation, between the convexity of the upper or large valve and the 

 area of the wing, being abrupt, well defined, and slightly oblique to the cardinal line; and 



1 Vide Plate XIV, fig. 34. 

 * King, Catalogue, p. 10. 



2 "Avicula testa subrhomboidali fornicata, ala antica rotundata postica falciformi producta, lineis con- 

 centricis regularibus." (Goldfuss, Petrefacta, 2d part, p. 126.) 



^ Denkschriften der KbnigUchen Akademie zu Miinchen, vol. vi, p. 30. 



