344 



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

 tricosa, rosacea, epidermide piceo induta ; margine ventrali in- 

 flecto, radiatim sulcato ; fastigio umbonali tumido, concentrice 

 undulato-striato : intus livescens ; cardine edentulo. Long. 3^ ; 

 alt. If ; lat. 1^- poll. Hah. 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 baud angulato, portione ligamentali arcuato ; 

 margine ventrali recto ; epidermide luteo-corneo postice fusces- 

 cente ; intus albida, postice livescens. Long. Ij^ ; alt. -^-^ ; lat. 

 I 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 distributed as in M. hamatus, but 

 are much larger. 



Mytilus algosus. T. transversa, subcylindrica, elliptico- 

 triangularis, valde erosa, epidermide tenui, intense smaragdino 

 induta ; margine dorsali angulato, postice ad marginem ventra- 

 lem rectum parallelo ; latere postico rotundato ; fastigio umbonali 

 tumido, obtuse ; cardine edentulo : intus punicea. Long. 1| ; 

 lat. f ; alt. f poll. Hah. 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 coerulea ; urnbonibus 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. 1^ ; 

 alt. If ; lat. ^ poll. Hah. Killimook, Puget Sound, Oregon. 



It is more slender and more cylindrical than 31. 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. 



