La ee 
ACEPHALA, A59 
Of the size and aspect of P. maximus and Magellanicus. The lower 
valve has the ribs like P. Jacobg@us, only they are not furrowed. 
Figures 569, 569 a, the two sides of the shell; 569, edge view of 
the shell. 
GAIMARDIA TRAPESINA (Gould). 
MopioLa TRAPESINA (Lamarck), Anim. sans Vert., vii. 24. DELESSERT; 
Recueil, pl. 13, f. 7. 
AnimaL with the mantle closed, except a small aperture at its 
anterior third, for the passage of the foot, a circular siphonal opening 
posteriorly, destitute of fringes, and a small excretory orifice just above 
and behind the posterior adductor muscle. Edges of the mantle 
yellow, destitute of any fringes or lobes. Branchize ample, the outer 
pair two-thirds the size of the inner, which cover nearly the whole 
space beneath the mantle, rounded at their free anterior end, and nar- 
rowing backwards; attached along the middle of the abdominal mass 
through their entire length. Mouth rather large, some distance above 
the base of the foot, with a short, compressed, labial appendage on each 
side. Foot linguiform, and capable of great extension, with a groove on 
the outer or ventral side; at its base are two convex lobes, which are 
emarginate on the posterior side; between, and at the junction of these 
lobes, at the emarginate part, is a conspicuous orifice, from whence 
proceeds the byssus, and which leads to a cavity occupying all the 
posterior portion of the foot, seeming to communicate with the visceral 
mass, by a small posterior puncture. Stomach large, extending across 
the liver; intestinal canal not traced, but the rectum appeared to tra- 
verse the heart, and to terminate just behind it; the heart itself is at- 
tenuated at both ends. Strie on the branchie very apparent. Liver 
chocolate-coloured, reticulated by numerous white fibres, divided into 
four lobes, two anterior and superior ones, separated by a deep longi- 
tudinal fissure, and two lateral and larger ones of an oval form; behind 
these, of a creamy colour and consistence, are the ovaries, constituting 
two-thirds of the whole abdominal mass. ‘The two adductor muscles 
are large for the shell. 
The animal moves with considerable rapidity, as follows: the foot 
is doubled, so that its point is brought to its base; it is then extended 
