212 MAZATLAN UNIVALVES 
Genus GADINIA, Gray. 
Phil. Mag. & Journ. 1824, p. 63:— Phil. Handb. Conch. 
p. 199.—H. g A. Ad. Gen. vol. i. p. 463. 
Mouretia, Sow. Proc. Zool. Soc. 1835, p.6:—Zool. Beech. Voy. 
p. 147. 
Pileopsis and Patella, sp. azct. 
270. GADINIA PENTEGONIOSTOMA, Sow. 
G.t. plus minusve conicd, seu valde depressd, alba; subcirculari, 
seu trregulariter varie angulatd ; apice subcentrali, in adulté 
detrito, in juniore spirali, anfractibus planorbiformibus, adver- 
sum cervicem lateraliter affixo; costis plurimis radiantibus, 
angustis, rotundatis, valde extantibus, interstitiis subequantibus ; 
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 outa 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. No very 
- young specimens were found, to compare with those 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, asin Siphonaria. The shell 
often begins very conical, and suddenly becomes flat. A 
regularly grown up sp. measures Jong. °68, lat. °63, alt, °18. 
The largest sp. Ai jy. 98, ge PBB ais. 48 
A flattened sp. FP i 2 Of, Peak eo 2 Lo 
