ACEPHALA. 449 
Length four and a half inches; height two and a half inches; 
breadth one inch. 
Inhabits New Zealand. 
Its general appearance is that of P. seminuda; but it is smaller, 
much darker, the ventral margin is less arcuated, and the scales much 
less numerous and regular. 
Figure 574, the shell. 
Myri.us pivaricatus (Gould). 
T. ovato-triangularis, arcuata, preter regionem byssicalem undique ra- 
diatim costato-sulcata, sulcis profundis, remotis, interdum divarican- 
libus ; apice peracuto, angulato ; margine dorsal haud angulato, por- 
tione ligamentah arcuato ; margine ventral recto ; epidermide luteo- 
corneo postice fuscescente: intus albida, posticée livescens. 
Mytilus dwaricatus, Goutp; Proceed. Boston Soc. Nat. Hist., ii. 
344. Dec. 1850. Expedition Shells, 94. 
Suey of medium size, rather solid, somewhat arcuately ovate-tri- 
angular; the apex very acute, divided by a sharp umbonal angle ; 
dorsal edge curved throughout, so as to exhibit but the vestige of an 
angle; ventral margin direct or slightly convex ; ventral edge lozenge- 
shaped, or somewhat tectiform. Surface, except the byssal region, 
deeply grooved radiately, the grooves often subdividing, forming pro- 
minent rounded ribs, diminishing ventrally. Colour yellowish, becom- 
ing dusky posteriorly. Interior whitish, or stained livid towards the 
dorsum. 
Length nearly two inches; height about one inch; breadth three- 
fourths of an inch. 
Inhabits the China Seas. 
In general aspect it is like M. Magellanicus, but is more angular, 
the grooves are deeper, more numerous and more generally distributed. 
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