MAZATLAN BIVALVES 99 
Differs from L. cancellaris in being much larger and flatter, 
with the teeth and lunule smaller in proportion. There is no 
posterior angle or flattening. The radiating ribs divide as in 
L. cancellaris, but the concentric ridges, instead of being 
sharp and standing so as to leave deep pits between, are very 
close and fine, running up and down across the ribs and inter- 
stices. It seems closely allied to L. fibula (St. Elena and 
Philippines), and to L. costata, D’ Orbigny, (Brazils.) Long. * 4A. 
tat.°49, alt. ‘16. 
Hab—Mazatlan ; one fresh valve and fragment, entangled in 
the byssus of Modiole ; L’pool Col. 
Tablet 470 contains the valve. 
143. Lucina cANCELLARIS, Phil. 
Zeit. f. Mal. 1846, p. 21, no. 7. 
Shell, when extremely young, smooth at the umbo, then 
with stout concentric ridges, then with 8 or 10 very strong 
radiating rounded ribs crossing them. These branch out into 
other narrower ones, till there are about 26, strongly caneel- 
lated, and leaving deep pits between. “The form closely 
resembles L. commutata, Phil., which is the real T. divaricata 
of Linneus. With L. pecten, squamosa and reticulata (Poli, 
not Lam.) it must not be confounded ; its strong rotundity, 
almost equilateral form, and the character of the sculpture at 
once distinguish them.” (Phil. loc. cit.) Lunule small, deep: 
posterior ligamental portion flattened, separated by an indis- 
tinct keel. Interior margin deeply crenated; muscular scars 
(anterior elongated, irregular) rather distant from margin; 
lateral and cardinal teeth strong. The smallest specimen is ‘03 
across. The largest, long. °15, lat. °14, alt. °09. 
Hab.—Mazatlan, Philippi.—Do.: extremely rare; L’pool Col. 
Tablet 471 contains the youngest valve and the largest pair. 
144. Lucina MAZATLANICA, 2. 8. 
Lt. parva, alba, suborbiculari, wmbonibus antice incurvatis, 
lunula longa, margine posticd obscure biangulato ; primum liris 
concentricis, acutis, plus minusve distantibus ; postea radits 
quoque rotundatis, creberrimis, ad marginem decurrentibus ; 
liris ad angulam posticam quibusdam obsoletis, reliquis extan- 
tibus ; area posticd subplanatd ; dentibus card. parvis, lat. sub- 
distantibus ; ligamento curto, subexterno ; impressionibus muse 
cularibus haud elongatis ; margine (haud semper) crenato. 
