MAZATLAN UNIVALVES 5OL 
vol. ix. p. 522, no. 31.—Val. in Humb. Rec. Obs. vol. i. 
p. 291.—Rve. Conch. Ic. pl. 9, f.20.—Mke. in Zeit. f. Mal. 
1851, p. 18, no. 84.—C. B. Ad. Pan. Shells, p. 127, no. 145. 
Cyrtulus patulus, Hinds, Voy. Sulph. Moll. p. 13. 
Cassidulus patulus, H. & A. Ad. Gen. i. 81. 
=P. melongena, var. Sow. Tank. Cat. p. 92, no. 1611. 
It is almost impossible to give characters by which all the 
specimens of this species can be distinguished from all the 
specimens of the W. Indian P. melongena. Deshayes says 
that they are best distinguished in the young state: yet one 
of the young specimens marked by D’Orbigny “‘P. melongena” 
in the Sagra Col. B. M. would certainly be called P. patula if 
the locality were unknown, as it agrees with this species in 
form, markings, and even in the remarkable epidermis: while 
another specimen in the same collection is of the true melon- 
gena type. ?It can scarcely be supposed that Sagra had 
obtained a West-coast shell. At the same time the general 
habit of the two species is sufficiently distinct, when taken in 
conjunction with the difference of ocean, to warrant their separ- 
ation, at least till their animals have been more carefully 
compared.* 
P. patula is generally distinguished (as compared with P. 
melongena,) by its much lighter, and somewhat slenderer 
growth. Of two shells, of almost exactly the same length, 
namely 5°3 inches, the breadth of P. melongena (without the 
spines) is 4°4, of P. patula only 3°9: also P. melongena weighs 
16° ounces, while the specimen of P. patula only reaches 5°5. 
Moreover P. patula in the adult is scarcely striated spirally 
or denticulated at the outer lip, (as in P. melongena,) except 
near the base. It has never more than one row of tubercles, 
on the shoulder, and these are often- evanescent. The colour 
is a deeper and richer brown ; generally with but few, or even 
without, spiral lines of light. Parietal infra-sutural callosity 
very slight. Posterior canal long, deep and narrow, (in the 
largest sp. Jong. 1°53, lat. °36, alt. °9,) more reflected over the 
spire, and producing a very concave surface outside. Labrum 
sharp. Labium thin, less expanded. The elevation of the 
spire is avery variable character. Epidermis extremely coarse 
_ and thick, in parallel shreds of growth, not unlike the husk of 
a cocoa-nut, but dull dark olive. The whole of the specimens 
* As specimens of the melongena type frequently occur in E. Indian collec- 
tions, and are so quoted by Reeve, ? are we to suppose that this species occurs 
in both oceans, or that a third species exists in the Indian Seas, 
