218 MAZATLAN UNIVALVES 



callus white, corruf?ated, not bordered. Differs from F. nigro- 

 punctata in the shape of the hole ; from F. virescens in this 

 and in the nigropunctation ; from F. alba in both characters, 

 in the green colour, and in the still more compressed growth 

 as compared with that species ; from F. nigrocincta, in the 

 green colour and absence of black ring ; from the conical 

 variety of F. rugosa in the regular growth, and nigropuncta- 

 tion, which is never seen in that variable species. The outside 

 not being in good condition, and the young of some of the 

 above species not having been observed, it is not thought 

 prudent to name it. Long.'b^, lat.'ZQ, alt. '2. (^iu. 90" by 85". 

 Sab. — Mazatlan ; 1 sp. only ; L'pool Col. 

 Tablet 1057 contains the specimen. 



276. FiSSUEELLA ALBA, n. S. 



F. t. ohlongd, compressa, conica, regulari, antice curtiori ; 

 alhd, rarius nigro radiatd ; liris radianiihus, subcequalibu^, 

 interdum Imvioribus, inferdum validis, valde nodulosis; aperturd 

 majore, oblongd, in medio const nctd, parietibus solidis, scppius 

 in medio elevatis ; intus albd, sen pallidissime earned, rarissime 

 vix viridi tinctd, nitente, scepius annulo nigro callositatem 

 oblongam cireumeunte, margine secundum liras crenulato, in 

 testa juniore scepe nigropunctata. 



Jun. ? = F. gemmata, Mke. Zeit.f. Mai. 1837, p. 186, no. 42, 



This well marked species is easily recognized by its elongated, 

 compressed, conical and regular growth. The young shell is 

 often rayed outside, and dotted in the inner margin with black : 

 else it is of a French white, or very pale flesh colour, glossy 

 inside ; rarely with a slight greenish tinge near the callus. 

 The ribs are gonci-ally rather fine and irregularly tuberculous ; 

 sometimes strong and nodulous ; very rarely slender and 

 almost smooth. The black band round the callus is usual, but 

 not constant. The F. gemmata of ilf/t-e., . described from a 

 single smtill shell, is pi-obably a rubbed young specimen of this 

 species ; but the diagnosis does not accord with sufficient 

 accuracy to adopt his name. The shells are generally more or 

 less incrusted with coralline, which often grows in irregular 

 longitudinal rays, occasionally meeting over tlie centre of the 

 hole, which they thus render bipartite. The aperture is large 

 and long ; its walls constricted in the middle and at the same 

 place elevated on each side. The smallest shell foimd, in 



