MAZATLAN UNIVALVES 501 



vol. ix. p. 522, no. 31. — Vaf. in Humh. Bee. Ohs. vol. ii. 



p. 291.— Rve. Conch. Ic. pi. 9, f. 2,0.-MJce. in Zeit.f. Mai. 



1851, p. 18, no. 81.— C. B. Ad. Pan. Shells, p. 127, no. 145. 

 Cyrtulas patulua, Hinds, Voy. Sitlph. Mull. p. 13. 

 Cassidulus patulus, H. Sf A. Ad. Gen. i. 81. 

 = P. melongeua, var. Sow. Tank. Cat. p. 92, no. 1611. 



It is almost impossible to give cliaracters by wbicli all the 

 specimens of this species can be distinguished from all the 

 specimens of the W. Indian P. melongeua. Deshayes says 

 that they are best distinguished in the young state : yet one 

 of the young specimens marked by D'Orbigny "P. melongcna" 

 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. Pit 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 waiTant their separ- 

 ation, at least till their animals have been more carefoliy 

 compared.* 



P. patula is generally distinguished (as compared with P. 

 melongeua,) 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. melongeua (without the 

 spines) is 4'4, of P. patula only 3 9 : also P. melongena weighs 

 16' ounces, while the specimen of P. parula only reaches 5 "5. 

 Moreover P. patula in the adult is scai-cely 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, spii'al lines of light. Parietal iufra-sutural callosity 

 very slight. Posterior canal long, deep and narrow, (in the 

 largest sp. long. 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 a very 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 tho melongena type frequently occur in E. Indian collec- 

 tions, nnd are so quoted by Ueevo, ? are we ti suppose that this species occurs 

 in both oceans, or that a tliird species exists in the Indian Seas. 



