888 MAZATLAN UNIVALVES 
Comp. Calypirea gemmacea, Val. Voy. Ven. pl. 15, f. 2. [Tf 
the figure be accurate, this is a distinct, tubercled species : 
but it may be a small, conical, worn C. imbricata; the quasi- 
tubercles being worn ribs. | 
The pitting of the intercostal spaces which seems to form the 
ground of separation between C. imbricata of Sow. and C. 
dentata of Mke. appears so very variable a character, that I 
have not ventured to regard them as distinct. The Mazatlan 
specimens (when in sufficiently fine condition to speak with 
certainty) are never wholly without pits: yet they are com- 
pletely irregular in their formation, often not being seen over a 
great portion of the surface ; not unfrequently appearing on one 
side only ; and very rarely traceable on the young shell. The 
species is normally rather solid, conical, with a very variable 
number (about 20) of stout rounded ribs, more or less spread- 
ing out at the margin. Fresh ribs are frequently formed in 
the intercostal spaces. When a fresh margin is formed below 
the palmations of the former one, a series of pits is produced. 
As the palmations are most developed in the adolescent state, 
so are the pits. They are rare in the older growth. Both ribs 
and intercostal spaces are finely, but irregularly indented with 
radiating corrugations. Fine radiating brown. lines are often 
traceable outside, dotting,the interior margin. The surface 
is generally rough and often covered aah accretions; the 
vertex is rarely preserved. 
In Mr, Darbishire’s collection, is a specimen with the animal 
matter dried within, and the young fry covering the principal 
part of the inner surface of the shell. These are shaped like 
Vanikoro, about ‘035 across; with the apex flat, not sunken ; 
with one tumid whirl exposed, and a very large umbilical area. 
The surface is concentrically and very finely furrowed. Most of 
the specimens have made a faint lip over the base, with an edge 
which is to commence the margin of the Patelliform shell; but 
the cup is not begun. In this stage, the shell cannot be dis- 
tinguished generically from Crepidula. The nuclear whirls are 
turned laterally with the plane of after growth (as in Capulus), 
perpendicularly to the base of the shell. The smallest specimen 
found in the adolescent stage is ‘17 across; at which period 
it greatly resembles the young of Crepidula dorsata, the ribs 
not beimg developed. The cup is then semicircular, produced 
in front, adhering at the two separate margins. As it inereases 
in size, the anterior margin bends round till it joins the 
posterior one, forming an entire cup, adherent almost to the 
