MYTILUS.— Plate X. 



Species 49. (Mus. Cuming.) 



MvTiLDS POLYMOKPHUS. Mi/t. testd trigono-lrapezoidea, 

 postice valde gibbosd, latisdme concavo-imprensd, ad 

 angnhim acuta, concentrice striata; luted, strigis 

 acute midatis olivaceu concentrice variegatd. 



The many-shaped Mytilus. Shell triangularly trape- 

 zoid, posteriorly very gibbous, very broadly coucavely 

 impressed, sharp at the angle, concentrically striated ; 

 yellow, concentrically variegated with zigzag olive 

 streaks. 



Pallas, It. Russ. vol. i. p. 478 ; Chemn. Couch, fab. 

 vol. xi. p. 256. pi. 20.5, pi. 202S. 



Mytilus Hagenii, De Baer. 

 Mytilus area, Kicks. 

 Dreissena polymorpha, Vanbeneden. 



Hah. Rivers of Northern Europe. 



This well-known species is distinguished from all others 

 of the Dreissena group by its extreme trapezoidal form 

 and variegated painting. 



Species 50. (Mus. Cuming.) 

 Mytilus cochleatus. Myt. testa elongalo-ohlongd, 



tice snhangulatd, postice impressd, concentrice striata ; 

 sordide fnscescente, purpurea concentrice strigatd. 



The spoon-shaped Mytilus. Shell elongately oblong, 

 anteriorly slightly angled, posteriorly impressed, con- 

 centrically striated ; dirty light-brown, concentrically 

 streaked with purple. 



Dreissena cochleata, Kickx, Dunker, MS. in ilus. Cuming. 



Hab. r 



Of a rather oblong-produced form, streaked with a 



characteristic pattern of concentric purple bands. 



Species 51. (Mus. Cuming.) 



Mytilus Moechianus. Myt. testd trigond, subcurvald, 

 postice subimpressd, umhonibus rostratis ; eroso-albd, 

 vpidermide lutescente fibrosd partim indutd. 



Morch's Mytilus. Shell triangular, slightly curved, 

 posteriorly faintly impressed, umboes beaked ; eroded- 

 «hite, partially covered with a yellowish fibrous epi- 

 dermis. 



Dreissena Morchiana, Dunker. 



Hab. Island of St. Thomas, West Indies. 



Of paler substance than usual in the Dreissena group, 



more or less invested with a yellowish fibrous epidermis. 



