CRENELLA. 195 



Mytilus and Modlola. For it we adopt the designation 

 given to Crenella decussata, by Brown, who, however, did 

 not perceive that he was constituting a genus, which really 

 belonged to the MytU'ida, and naturally included several of 

 the shells ranked by himself as Modioli. The uncharac- 

 terized genera Modiolarca, of Gray, and Modiolaria, of 

 Beck, seem to be synonymous, certainly the latter, with 

 Crenella in the extended sense in which we propose to 

 adopt it. The members of the genus are very elegant 

 little shells, and great favourites with collectors. The 

 habit of boring into the test of Ascidia, indicates an 

 affinity, evident also, on comparison of shell and animal, 

 with LitJiodomus. 



C. discoks, Linnaeus. 



Moderately ventricose, not marbled, smooth in the middle, 

 rayed with impressed lines (occasionally almost obsolete poste- 

 riorly) at the sides ; hinder area elevated, somewhat lobated 

 below. 



Plate XLV. fig. 5, 6, and Plate XLVIII. fig. 5. 



Mytilus discors, Linn. Syst. Nat. ed. 12, p. 1159 (from type). — Loven, Index 

 Moll. Skandinav. p. 33. 

 „ discrcpans, Mont. Test. Brit. p. 169.— Turt. Conch. Diction, p. 112. — 



Dillw. Recent Shells, vol. i. p. 319. 

 „ discors, var. /3. Maton and Rackett, Linn. Trans, vol. viii. p. Ill, 

 pi. 3, f. 9. 

 Modiola discrcpans, Lamarck, Anim. s. Vert. (ed. Desh.) vol. vii. p. 23. — 

 Turt. Dithyra Brit. p. 202. — Forbes, Malacol. Mo- 

 nensis, p. 44. — Brit. Marine Conch, p. 108 (chiefly). — 

 Alder, Cat. Moll. Northumb. and Durh.p. 81. — Gould, 

 Invert. Massach. p. 129, f. 83 (probably). — Hanl. Recent 

 Shells, vol. i. p. 242. 

 (Unnamed.) Brown, 111. Conch. G. B. pi. 39, f. 36. 

 ? Modiola minuta (fry), Couch, Cornish Fauna, pt. 2, p. 33 (not described). 



A careful examination of the Linnsean cabinet enables us 

 to state positively, that this is the species intended by the 



