572 MOLLUSCA. 
of normal specimens of P. montagnei some feeble spiral ridges are visible on the last 
whorl just above the basal keel, causing slight nodules by crossing the ribs. In the 
var. pulcher it is usually the last whorl also which shows the cancellated sculpture 
more conspicuously, but in its whole extent between the suture and the basal keel, 
whereas in the penultimate and antepenultimate whorls the spiral ridges are very faint, 
if they exist at all. Whether the presence of varices is constantly united with a 
distinct cancellated structure of the last whorl, I cannot decide, having but few 
specimens before me. The form and colour of the aperture is in the var. pulcher 
quite as in the normal P. montagnet. 
N.B.—Cerithium largillierti, Philippi (Zeitschr. f Malak. 1848, p. 20; Abbild. neuer 
Conch. iii. p. 15, t. 1. fig. 7)= Cerithidea fortunet, Reeve (Conch. Icon. xv. t. 3. fig. 15 a), 
from China, is incorrectly quoted by Reeve as synonymous with C. montagnei. 
3. Potamides costatus. (Tab. XLIV. figg. 11, 11a.) 
Strombiformis costatus, Dacosta, Brit. Conch. p. 118, t. 8. fig. 14 (1778) °. 
Strombus costatus, Montagu, Test. Brit. 1. p. 255 (1803) *. 
Cerithium costatum, Forbes & Hanley, Hist. Brit. Moll. in. p. 20°; Kobelt,in Martini & Chemnitz, 
Syst. Conch.-Cab. ed. 2, Cerithium, p. 179, t. 33. fig. 10°. 
Cerithidea costata (Dacosta) (part.), Tryon, Manual of Conch. ix. p. 164, t. 34. fig. 82 (copied 
from Reeve) ’. 
Cerithium salmacidum, Morelet, Test. Noviss. 1. p. 27 (1849)°; Kobelt, loc. cit. p. 68, t. 12. 
fige. 8, 9 (not quite full-grown) *. 
Cerithidea salmacidum, Morch, Malak. Blatt. xxii. p. 90 (1876) °; Reeve, Conch. Icon. xv., 
Cerithidea, t. 4. fig. 23 (salmacida) *. 
Turrited, very slender, with deep sutures, dark brown; 12 whorls, very convex, in some specimens nearly 
biangulated ; ribs perpendicular, numerous, about 33 in the penultimate, only 26 in the antepenultimate 
whorl, swelling into two small knobs in some specimens at the crossing of the subangular spiral elevations ; 
on the last whorl, on the contrary, the ribs are much more feeble and irregular, wanting here and there; 
the periphery of the last whorl encircled by a feeble spiral keel, which in some specimens is followed by 
another lower and more feeble one; the rest of the basis without spiral ridges. Usually without varices. 
Aperture with somewhat vaulted, but scarcely thickened peristome. Operculum circular, a little concave, 
with many whorls; the nucleus near its middle, the margin very thin, diaphanous. 
Long. 13-14, diam. 5-5}, long. apert. 33 millim. 
Hab. Yucatan: Sisal, in swamps of the sea-shore (Morelet*); Progreso (Hége) ; 
Yucatan, without nearer indication of locality (Poulsen *, H. Dohrn’). 
Also on the shores of the West-Indian Islands 34, but not British as had been 
formerly supposed ! ?, 
The above description is taken from a choice of the most perfect and best-preserved 
specimens out of a great number collected by Herr Hoge at Progreso, none of which 
measure 17 millim., the length assigned to the species by Morelet ®. In most of them 
there are no varices at all, but in some there is a single varix on the last whorl, quite 
near the aperture, perhaps a duplication of the peristome; it is, however, of the same 
