ACEPHALA. 453 
edge rectilinear, about half its length, then gradually curving; tip 
broadly rounded ; ventral margin concave near the beaks, where there 
is a large fissure for the byssus; a constriction, running from the 
beaks to the end of the fissure, marks off a triangular segment of a 
darker colour; epidermis thick, varnished, of a deep chestnut-brown, 
paler along the umbonal ridge, marked by undulations of increment, 
and indented with numerous short, arrow-headed, radiating undula- 
tions: interior cream-colour, livid around the ligament, the dorsal 
portion flesh-coloured. 
Diameters: longitudinal, two inches; vertical, an inch and a quar- 
ter; transverse, one inch. 
Inhabits New Zealand. 
Somewhat like M. vulgaris; the beaks are nearly terminal, the 
byssal opening broader and nearer the beaks, the ventral margin arch- 
ing inwards instead of outwards at this point; the epidermis is darker 
and more shining, and the nacre is different. 
Figures 562, 562a, lateral and dorsal views of the shell. 
Myrinus (Modiola) rLABELLATUS (Gould). 
T. transversa, elongata, trapezoidea, trifariam cuneata ; apicibus mi- 
nime terminalibus, acutis, attigentibus ; dechivitate umbonah ventri- 
coso, angulato; marginibus rectilinearibus ; latere postico oblique 
truncato, haud angulato ; epidermide anticé nitido, exusto, posticé 
flavo-viridi, flosculis rigido: intus exalbida. 
Mytilus (Modiola) flabellatus, Goutp ; Proceed. Boston Soc. Nat. 
Hist., iii. 343. Dec. 1850. Expedition Shells, 343. 
SHELL large, thin, elongated, trapezoidal, dilated posteriorly ; beaks 
elevated, pyramidal, contiguous, acute, placed at the anterior seventh ; 
umbonal ridge elevated, angular above, widening and becoming more 
rounded backwards; portion anterior to the slope trigonal, wedge- 
shaped in three directions; extremity narrow, rounding upwards ; 
dorsal and ventral margins diverging, rectilinear for three-fourths of 
114 
