218 MAZATLAN UNIVALVES 
callus white. corrugated, 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 tonameit. Long. °55, lat. *36, alt. °2. div. 90° by 85°. 
Habh—Mazatlan ; 1 sp. only ; Z’pool Col. 
Tablet 1057 contains the specimen. 
276. FIssURELLA ALBA, %. s. 
F. t. oblonga, compressd, conica, regulari, antice curtiori ; 
albé, rarius nigro radiata; liris radiantibus, subequalibus, 
interdum levioribus, interdum validis, valde nodulosis; apertura 
majore, oblonga, in medio constrictd, parietibus solidis, sepius 
zn medio elevatis ; intus alba, seu pallidissime carned, rarissime 
vie viridi tinctd, nitente, sepius annulo nigro callositatem 
oblongam circumeunte, margine secundum liras crenulato, im 
testa juniore sepe nigropunctata. 
Jun. ?=F. gemmata, Mike. Zeit. f. Mal. 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 generally 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 Méze., described from a 
single small shell, is probably 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 inerusted with coralline, which often grows in irregular 
longitudinal rays, occasionally meeting over the 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 eleyated on each side. The smallest shell found, in 
