ACE PHA L-A 451 
nibus remotis excurvatis, 5-denticulatis ; marginibus sub-parallelis ; 
margine ligamentali adscendente, recto, angulato ; fastigio umbonal 
tumido, obtuso ; intus cretato, limbo atro ; cicatrice palleali lineart. 
Mytilus trossulus, Goutp; Proceed Boston Soc. Nat. Hist., ill. 344. 
Dec 1850. Expedition Shells, 94. 
Suet small, glossy, crow-black, elongated, narrow, marked only 
with fine undulations of growth: ventral margin direct: dorsal margin 
obtusely angular at the middle, the posterior portion declining a little 
towards the base: end rounded, forming a very small, triangular 
dorsal wing; umbones tumid: basal aspect a little flattened : interior 
chalky, bluish-white; margin inky black : muscular impression nar- 
row, and separated from the limbus by a mere thread throughout: 
hinge denticles, about five: beaks sharp, on a level with the base. 
Length an inch and a quarter; height an inch and three-fifths ; 
breadth half an inch. 
Inhabits Killimook, Puget Sound, Oregon. 
Differs from M. edulis in its more elongated and more cylindrical 
form: the dorsal wing is less elevated, its posterior slope rectilinear, 
and not curved: colour more glossy black, and without radiating 
strie; and interiorly it has a threadlike separation of the muscular 
impression from the dorsal limbus, instead of a rapidly widening one 
as in M. edulis. It is barely possible to be the same. It accords 
pretty well with the figure given by Middendorff as M. edulis (Bei- 
trage, &c., pl. xiv., f. 7, 8). 
Figure 567, lateral view of the shell, exterior and interior; 567 a, 
dorsal view. 
Myvitus pyriFormis (Gould). 
T’. solida, elongata, ovato-trigona, ventricosa, rosacea, epidermide piceo 
induta; margine ventrali inflecto, radiatim sulcato ; fastigio umbonah 
tumido, concentrice undulato-striato: intus livescens ; cardine edentulo. 
