212 MAZATLAN UNIVALVES 



GENUS GADINIA, Gray. 



Phil. Mag. & Journ. 1824, p. 63: Phil. Handb. Conch. 



p. 199. H. $ A. Ad. Gen. vol. i. p. 463. 

 Mouretia, Sow. Proc. Zool. Soc. 1835, p. 6 iZool. Beech. Toy. 



p. 147. 

 Pileopsis and Patella, sp. auct. 



270. GADINIA PENTEGONIOSTOMA, Sow. 



6r. t.plus minusve conicd, seu valde depressd, albd; subcirculari 9 

 sew irregulariter varie angulata ; apice subcentrali, in adultfi, 

 detrito, injuniore spirali, anfractibus planorbifonnibus, adver- 

 sum cervicem later aliter affixo ; costis plurimis radiantibus, 

 angustis, rotundatis, v aide ext ant ibus, inter stitiis subcequantibus ; 

 margine costis productis, cavatis, subdiaphanis ; canali minima, 

 ad marginem haud extante ; cicatrice musculari dextrorsum 

 integro, sinistrorsum irregulariter lobato. Animal cavitatem 

 corrodente. 

 Siphonaria pentegoniostoma, Sow. ? ubi. 



Having met with no description of this shell, the name of 

 which is likely to mislead, I have drawn out a diagnosis from 

 a comparison of several hundred specimens. Most of the shells 

 are very irregular in growth, apparently crowding each other 

 and forcing their bodies into angular shapes : but the normal 

 condition appears to be nearly round, with semi-transparent, 

 hollowed, projecting ribs. The muscular scar, on the opposite 

 side from the slit, is irregularly divided into lobes. The mus- 

 cle of attachment appears very strong, the shell being generally 

 broken in removal; and on the place of adhesion (which is 

 eaten away) is generally seen a black circular ring. JS"o very 

 young specimens were found, to compare with tlfose of Siphon- 

 aria: but on the smallest, '23 in length, is just discernible a 

 . small planorbiform apex, turned to one side, away from the 

 head ; in this respect agreeing with Siphonaria and differing 

 from Patella. The ribs are of nearly equal size, there being 

 no large one to receive the canal, as in Siphonaria. The shell 

 often begins very conical, and suddenly becomes flat. A 

 regularly grownup sp. measures long. *68, lat. '63, alt. '18. 



The largest sp. \ ' '98, '88, '43. 



A flattened sp. '67, '53, '16, 



