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. '44, 

 lot. '49, alt. '16. 

 Hab. Mazatlan ; one fresh valve and fragment, entangled in 



the byssus of Modiolse ; Lpool Col. 



Tablet 470 contains the valve. 



143. LUCINA CANCELLARIS, Phil. 



Zeit.f. Mai. 1846, p. 21, no. 7. 



Shell, when extremely young, smooth at the umbo, then 

 with stoi.it 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 cancel- 

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

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

 of Linnaeus. 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, lot. '14, alt. '09. 

 Sab. Mazatlan, Philippi. Do. : extremely rare ; L'pool Col. 



Tablet 471 contains the youngest valve and the largest pair. 



-/-" 144. LUCINA MAZATLANICA, n. s. 



L. t. parvd, albd, suborbiculari, umbonibus antice incurvatis, 

 lunuld longd, tnargine posticd obscure biangulato ; primum liris 

 concentricis, acutis, plus minusve distantibus ; postea radiis 

 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 ; impression^ us mus- 

 cularibus haud elongalis ; margine (haud semper) crenato. 





