Morxi.i A. 



the grtfiote-oorrugation b or lenzig-xagorcriit- 



oi tin- central arras, illijm-ly r..migated-grano8e on the 



lateral aivas. /nt<ri<>r \rhil>\ "/'//, /<or< cr/' 



; tail -inn- visiMr outside. (iinll.- with fi-w and .-hurt I. 



hinil.<ii . Si,\vl. in Mus. Cuming) lii ndi. I-.,n., t. 



11'. f. 117.1, b (1847). Mopnlin /ihul.n ( i KA Y, I'. /. S. 1M7, pi 

 169. II. it A. AD., Genera Rec. Moll, i, p. 478, iii, t. 54, f. 7. 

 MnjHtlia ritinta rur. Itindsii DALL, Proc. U.S. Nat. Mus. 187> 

 304. 



The specimens described are from San Francisco Bay. The teg- 

 mentum or outer layer of the valves projects forward somewhat at 

 the sinus, as in typical nmscosa^ but this can be seen only in the 

 detached valves. 



Var. PORIFERA Pilsbry. PI. 62, figs. 93, 94. 



Another form of muscosa, which if constant in its peculiar features 

 would make an excellent new species of the section 0teochiton, is 

 before me from Boliuas Bay. It is perhaps deserving of a varietal 

 name. The shell is rather small, thin and high, but not to as great 

 an extent as M. acuta. It is sculptured as in M. hindsii, but the 

 diagonal and sutural ribs are more prominent, and sculptured with 

 strong, transverse beads exactly as in M. imporcata, the suture being 

 dentated by them. Color of valves olivaceous, clouded obscurely 

 with smoky, and having a black stripe each side of the dorsal 

 lighter stripe. The posterior valve has a depressed mucro near the 

 posterior margin, which is very slightly waved inward. Girdle 

 firm and leathery, minutely and evenly papillose all over, blackish 

 with spots of orange ; having a small pit or pore at each suture, with 

 a series of pores alternating with these a little outside of the middle 

 of the girdle (pi. 62, fig. 93). Sometimes some of the sutural pores 

 bear large hairs, curling outward; and sometimes some or many of 

 the pores are completely absent. 



Length 23, breadth 13* mill.; divergence 105-115. 



The interior is a deep blue-green, or gray-blue \vith a purple-pink 

 blush. 



Var. ACUTA Carpenter. PL 64, figs. 75-81. 



Shell rather small, strongly elevated, the dorsal ridge acute : 

 valves thin ; sculpture minute and delicate, varying between a 

 minute granulation and a fine pitting; the sutures delicately dentic- 



