91 



Mytilus pyriformis. T. solida, elongata, ovato-trigona, ven- 

 tricosa, rosacea, epiderrrr^e piceo induta ; margine ventrali in- 

 flecto, radiatim sulcato ; fastigio umbonali tumido, concentrice 

 undulatostriato : intus livescens ; cardine edentulo. Long. 34 ; 

 alt. If ; lat. H poll. Hal. South Seas. 



The similarity of the dorsal and ventral curves ; its inflated 

 ventral portion, its great lateral diameter, its peculiar coloration 

 and striation are well marked. 



Mytilus divaricatus. T. ovato-triangularis, arcuata, prseter 

 regionem byssicalem undique radiatim costato-sulcata,sulcis pro- 

 fundis, remotis, interdum divaricantibus ; apice peracuto, angu- 

 lato ; margine dorsali haud angulato, portione ligamentali arcuato ; 

 marline ventrali recto ; epidermide luteo-corneo postic: fWces- 

 cente ; intus albida, postice livescens. Long. Ijjj ; alt. y 9 ^ ; lat. 

 £ poll. Hah. China Seas. 



In general aspect it is like M. Magellanicus, but is more angu- 

 lar, the grooves are deeper, more numerous and more generally 

 distributed. The grooves are disposed as in M. hamatus, but 

 are much larger. 



Mytilus algosus. T. transversa, subcylindrica, elliptico- 

 triangularis, valde corrosa, epidermide tenui, intense smaragdino 

 induta; margine dorsali angulato, postice ad marginem ventra- 

 lem rectum parallelo ; latere posticorotundato ; fastigio umbonali 

 tumido, obtuso ; cardine edentulo : intus punicea. Long. If ; 

 lat. f ; alt. | poll. Hob. South Seas. 



The slender cylindrical form, very dark green epidermis and 

 interior coloration are good diagnostic characters. 



Mytilus trossulus. T. parva, elongata, subarcuata, nitida, 

 coracina, subtus ccerulea ; umbonibus remotis excurvatis, 5-den- 

 ticulatis; marginibus sub-parallelis ; margine ligamentali ad- 

 scendente, recto, angulato ; fastigio umbonali tumido, obtuso ; 

 intus cretato, limbo atro ; cicatrice palleali lineari. Long. \\; 

 alt. 1-g ; lat. I poll. Hub. Killimook, Puget Sound, Oregon. 



It is more slender and more cylindrical than M. edulis ; the 

 dorsal wing is less elevated, the posterior slope rectilinear ; the 

 color is more glossy jet-black and without radiations, and there 

 is a difference in the form of the muscular impression. 



