M Y T I L U S . 



Genus MYTILUS, Lmnaiis. 

 Tesla aqnivalvis, oblique flahelUformu, plm minus trigona, 

 hysso affixa, umbmibus acutis, subreciis, terminaU- 

 bus ; latere antico smpe contpresse expama, podico 

 siibconlracto ; epidermide plerutiique cornea, interdum 

 pilosd. Cardo edentulus, inderdnm. smbcrenulatvs, li- 

 gamenfo marginali, subintcrno. Impressio muscularis 

 composita, sublaleralis. 

 Shell equivalve, obliquely fan-shaped, more or less trian- 

 gular, affixed by a byssus, umboes sharp, nearly 

 straight, terminal ; anterior side often conipressly ex- 

 panded, posterior somewhat contracted ; epidermis 

 generally horny, sometimes hairy. Hinge toothless, 

 sometimes slightly crenulated, with the ligament 

 marginal and partially internal. Muscular impres- 

 sion compound, sublateral. 

 The Mi/tili are chiefly characterized by an elongately 

 fan-shaped growth, more or less beaked towards the um- 

 boes, having the interior side for the most part compressly 

 expanded and the posterior arcuately contracted. Some 

 species, distinguished by the presence of a thin shelf across 

 the interior of the umboes, are arranged by authors as a 

 separate genus under the name of Septifer ; and others, 

 characterizetl by a not unimportant diiferenee in the ani- 

 mal, have been separated under the name of Dreissena. 

 Neither of these forms iiave been however allowed to take 

 are rank of genera by Deshayes. 



So much do the Mytili vary in appearance under diffe- 

 rent circumstances of habitation, as exemplified by the two 

 figures of M. Ualifornianus in the accompanying Plate, 

 that it has been impossible to identify many of the species 

 described by Continental conchologists. Sixty-one are 



all that have been satisfactorily made out by procurable 

 specimens ; their range of habitation extends over the seas 

 of both hemispheres. 



Fig. 1. (Mus. Cuming.) 

 This delicately-formed and exquisitely-coloured shell is 

 the Mytilus flams of Poll, now universally regarded as a 

 variety of M. edidis, for description of which see PI. VIII. 

 Sp. 33. 



Species 2. (Fig. 2 a, b, Mus. Cuming.) 

 Mytilus Californianus. Mijt. tesld pyriformi-elongatd, 

 snbarcuatd, solidd, radialim costatd, snick intermediii 

 conspiciie excavatis, concentrice rude comtgatd, area 

 posticd Icevigatd ; luteo-oUvaced, in (elate nigricante- 

 carnled. 

 The Californian Mytilcs. Shell pyriformly elon- 

 gated, slightly arched, solid, radiately ribbed, inter- 

 mediate grooves conspicuously excavated, concentri- 

 cally rudely wrinkled, posterior area smooth; yel- 

 lowish-olive, blackish-blue with age. 

 Conrad, Journ. Acad. Nat. Sci. Philadelphia, vol. vii. 



p. 242. 

 Hab. California. 



The examples here figured of this fine species represent 

 its extreme states. Young specimens, as Fig. 2 b, are 

 rayed with strongly excavated grooves, and the shell is of 

 a rich yellowish-olive eolonr. In a more advanced state, 

 the grooves become more and more obsolete, and the shell 

 assumes a rough blackish-blue tone. 



January, 185S. 



