1909.] NATURAL SCIENCES OF PHILADELPHIA. 529 



and figured (see Nautilus, Vol. 21, figs. 4, 8 and 9 of pi. 5). They are 

 more acute in the spire and thinner than typical vallesensis, also smaller. 

 The shells taken the past winter were from farther up the stream than 

 those taken two years before. Not one could be found at the place 

 where they were then. 



Chaimai Creek is about two miles down the Valles River from the 

 Willis ranch (where typical P. vallesensis occurs), and begins with a 

 spring about a mile from the river. The water of the spring is a little 

 warm and the pool there contains no Pachycheilus. Lower down they 

 were often on and among decaying leaves. 



Pachycheilus suturalis n. sp. PI. XXIV, figs. 16-20. 



The shell is turrited, regularly and slowly tapering, moderately solid 

 though rather thin, black, blackish-brown or brown. In perfect 

 shells the first (embryonic) 2% whorls are smooth and convex; four or 

 five following whorls have an acute carina below the middle, with an 

 acute thread above and one below it ; on subsequent whorls the carina 

 is reduced and the number of spiral threads increases, so that there is 

 a brief stage of about one whorl where the convex surface has about 

 6 subequal spirals; the lower spirals then diminish, leaving the last 

 3 or 4 whorls nearly smooth except for a group of usually three or four 

 spiral cords just below the suture. Some weak traces of spiral stria? may 

 often be seen on the smoothish portion, under the lens. The aperture 

 is broadly ovate, narrower above, but rounded there in adults, broadly 

 rounded below. The peristome is thin, blackish, noticeably retracted 

 just below the columella, and the outer lip is sinuous, being somewnat 

 retracted above. The parietal callus is brown or blackish, rather 

 heavy. 



Length 28, diam. 13, aperture 11 mm.; whorls remaining 5+. 

 " 28, " 1H, " 11 " " " ~ 6|. 



" 24^ " 11, " 10 " " " 6*. 



26, " 11£, " 9i " " " 7. 



Creek near Tampamolon, with P. pleurotoma. Also found in the 

 creek at Coxcantlan, a creek one mile above the ford of the Moctezuma 

 River, and in the first and second brooks crossed on the road through 

 the mountains to the Moctezuma River; all in the State of San Luis 

 Potosi. 



This species is related to P. pleurotoma, which differs chiefly by its 

 Pleurotomoid sinus. The only other related species is P. saussurei 

 (Brot), 3 of which two of the original lot, received from Dr. Brot, are 



3 See Kuster's Conchylien Cabinet, Melanaceen, p. 43, pi. 5, fig. 7; type locality 

 a swamp in the woods bordering the Rio Grande , which empties into the Lagnna 

 de Meztitlan, State of Hidalgo. It has no outlet to the sea. 



