MAZATLAN BIVALVES 99 



Differs from L. cancellaris in being mneh 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, IfOrhigny, (Brazils.) Long. "44. 

 lat. -49, alt. '16. 



Sab. — Mazatlan ; one fresh valve and fragment, entangled in 



the byssus of Modiolae ; IS pool Col. 



Tablet 470 contains the valve. 



143. LUCINA CANCELLAEIS, TTlil. 



Zeit.f. Mai. 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 nan-ower ones, till there are about 26, strongly cancel- 

 lated, and leaving deep pits between. "The form closely 

 resembles L. coramutata, Phil., which is the real T. divaricata 

 of Lmnseus. 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. Ltjcina Mazatlanica, n. s. 



L. t. parvd, alba, suhorbiculari, umbonibw! antice incurvatis, 

 lunula longd, margine posticu obscure biangulato ; primum liris 

 coneentricis, acutis, plus minusve distantibus ; postea radiis 

 quoque rotundatis, n'eberrimis, ad marginem decutTentibus ; 

 liris ad angulam posiicam quibusdam ohsoletis, reliquis extan- 

 tibus ; area posticu subplanatd ; dentibus card, parvis, lat. sub" 

 distantibus ; ligamento curto, subexterno ; impressionibus mus- 

 cularibtis haud elongatis ; margine (haud semper) crenato. 



