POTAMIDES. 573 
colour’ as the rest of the surface, not whitish or white, as in P. iostomus, Pfr., and 
ih varicosus, Sow. Many of the Progreso shells are not full-grown, with a very thin 
simple peristome, like the specimen figured by Kobelt’. Others are more or less 
worn, with the ribs scarcely visible or absent. 
The description given by Forbes and Hanley * applies so well to the specimens before 
me that I have no hesitation in referring them to P. costatus. As regards P. lafondi, 
Michaud, and P. ambiguus, C. B. Adams, I am not satisfied concerning their identity, 
or as to how they differ from P. costatus, various forms being labelled with these 
names in collections; Kiener’s figure of P. lafondi (Iconographie, Cerithium, t. 24. 
fig. 3) and Reeve’s figure of P. ambiguus (Conch. Icon. xv., Cerithidea, t. 2. figg. 9 a, b) 
appear to me to differ from P. costatus, as well as from one another. 
Dr. Morch § and Kobelt 4? treat P. salmacidus * and P. costatus as distinct species. 
4. Potamides tenuis, 
Potamides tenuis, Pfeiffer, in Archiv f. Naturg. 1839, p- 537°, 
Cerithidea tenuis, Reeve, Conch. Icon. xv., Cerithidea, t. 1. fig. 3°; Morch, Malak. Blatt. xxi. 
p. 87°. 
Cerithium (Cerithidea) tenue, Kobelt, in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, p. 181, t. 33. 
fig. 13 *. 
Potamides scalariformis (part.), Tryon, Manual of Conch. ix. p. 163, t. 33. fig. 76 (copied from 
Reeve) ’. 
Conico-turrite, with deep sutures and without varices, dark brown ; ribs in the whorls, except in the last two, 
rather strong, smooth, and a little oblique, 20 in the antepenultimate whorl—-in the last two they are 
somewhat more feeble, a little knobbed (nodulose), and more numerous, 26 in the penultimate, 34 in the 
last whorl ; there are usually three small knobs on each rib, the two lower ones the most distinct ; three 
darker brown spiral bands in the last two whorls, these corresponding to the small knobs of the ribs, but not 
forming raised lines in the intervals between the ribs ; three raised spiral lines at the lower angle of the 
last whorl and four or more thinner ones at the lower face of it. Outer margin of the aperture expanded 
and a little vaulted, but scarcely thickened ; outside of a yellowish-brown colour, a little paler than the 
_ rest of the shell, inside whitish ; inside of the aperture farther within dark brown. 
Long. 23, diam. (incl. peristom.) 8; apert. long. 6, diam. 4 millim. 
Hab. Norru America: Florida (Mus. Berol.). 
S.E. Mexico: Teapa, State of Tabasco (H. H. Smith). 
Cusa (Pfeiffer, Gundlach). 
The above description is made from the single example obtained by H. H. Smith at 
Teapa; it agrees in all essential points with others from Cuba and Florida in the 
Berlin Museum. In the published descriptions and figures the difference in the form 
of the ribs of the last two whorls is not so clearly indicated as I find it in the specimens 
before me. 
N.B.—Potamides scalariformis, Say (1825), from “ the freshwater lakes of Florida” 
* « Salmacidus” is a Latin adjective, used by Pliny, and meaning “a little salted”; “ Salmacis” is a 
better-known mythological name of a nymph (Ovid, Metamorph. iv. 286 e¢ seq.). 
