452 MOLLUSCA. 
Mytilus pyriformis, GOULD ; Proceed. Boston Soc. Nat. Hist., iii. 
344. Dec. 1850. Expedition Shells, 94. 
Suet large, solid, transversely ovate triangular: anterior portion 
acutangular, dorsal margin very slightly arcuated very near beaks, at 
its posterior third a little angular: posterior end rather shortly rounded : 
veutral margin gently convex throughout: surface faintly grooved 
radiately, the grooves quite conspicuous on the umbonal ridge, which 
runs quite low down, is very tumid and obtuse, making the ventral 
portion much more full than the dorsal: the concentric grooves of 
growth are coarse and undulating: colour of shell faintly rose red: 
epidermis very thick, fragile, pitchy black: interior livid white. 
Length three and a half inches; height one inch and three-fourths ; 
width an inch and a half. 
Inhabits the South Seas. 
One of the peculiarities of this shell is the similarity of the curve of 
the dorsal and ventral margins, giving it, when viewed internally, an 
elongated egg-shape. Its inflated ventral portion, and its striation and 
coloration, are also marks easily recognised; its lateral diameter is 
unusually great. 
Figures 564, 564 a, lateral and dorsal views of the shell. 
Myritus (Modiola) aREOLATUS. 
Testa transversa, ovato-elongata, incurvata, tumida ; apicibus approxt- 
matis, angulalis, feré terminalibus ; margine dorsal arcuato ; mar- 
gine ventral fornicato, valde hiante ; epidermide nitido, castaneo, 
portione antico-ventrali sulco limitato: intus alba, limbo dorsal pur- 
purascente. 
Mytilus (Modiola) areolatus, Gou.p; Proceed. Boston Soc. Nat. 
Hist., ii. 343. Dec. 1850. Expedition Shells, 93. 
Suet rather solid, transversely ovate, umbonal end pointed and 
decurved; beaks very near the tip, tumid, obtusely angular; dorsal 
