132 HELIX-OXYCHONA. 



mus pileiformis PFR. Symb., p. 120. Geotrochus pileiformis BECK, 

 Index p. 47. H. pileiformis REEVE, Conch. Icon., f. 589. 



May be separated from If. gyrina by the pervious umbilicus, not 

 closed by the expanded columellar lip. It is more elevated than 

 the other species of Oxychona. 



H. ZHORQUINENSIS Angas. PI. 60, figs. 12. 



Narrowly rimate, trochiform, with straight lateral outlines, acutely 

 carinated periphery and nearly flat base ; thin, slightly translucent, 

 pale yellowish green, with a narrow, well-defined deep chestnut 

 brown band around the middle of the upper surface of each whorl 

 except, the apical two or three, and a very narrow subsutural brown 

 line which continues to the apex and is broader there, The spire 

 is conical, nearly straight-sided ; whorls 5 to 6 ; the apex is blunt, 

 polished, chestnut and corneous ; the first two whorls are glossy, con- 

 vex, with deep sutures ; the remaining whorls are nearly lusterless, 

 and covered with an extremely minute decussated pattern of very fine, 

 dense, spiral and oblique impressed lines ; lower two whorls plane, 

 with linear sutures ; last whorl not descending at aperture, acutely 

 keeled at the periphery ; base concave below the keel, then slightly 

 convex in the center ; aperture oblique, trigonal, showing the bands 

 inside, expanded ; peristome thin, acute, white, expanded all around, 

 especially at the position of the peripheral keel ; basal margin briefly 

 reflexed, suddenly widened at the insertion into a little triangular 

 plate which almost covers the narrow umbilicus. 



Alt. 21, diam. 25 mill. 



Along the Zhorquin River, Costa Rica. 



H. (Oxychona) zhorquinensis ANGAS, Proc. Zool. Soc. Lond. 1879, 

 p. 475, t. 40, f. 1. 



" Animal very slender, nearly white, pale brownish on head and 

 top of body." (Gabb.) 



A species of elegant outline and coloration, allied to H. bifasciata, 

 but larger, with finer sculpture, more expanded lip, and pervious 

 umbilicus. The peristome is rostrated or beaked at the position of 

 the peripheral keel ; the band of the upper surface stops about 3 

 mill, short of the edge of the lip, as it does in H. bifasciata. 



*** 



H. TRIGONOSTOMA Pfeiffer. PI. 14, figs. 1, 2, 3, 4 ; pi. 18, figs. 1, 2. 



Imperforate, trochoidal, with rounded or bluntly angled periphery 



and convex base ; thin but rather strong, white, spirally banded 



