276 CALIFORNIA ACADEMY OF SCIENCES. 



The above is the original description by Gould. Tnrbonilla fPyrgiscusJ 

 tenuiculn Gould is the most abundant and most variable species of all the west 

 American forms, presenting many varieties or incipient species; to describe these 

 would not aid science or the collector, but would only add to the confusion which 

 this paper is intended to dispel. The following comprehensive description will 

 embrace, we believe, all the forms coming under this name: — 



Shell slender to somewhat stubby and inflated, varying in color from milk-white to waxy 

 yellow or to dark brown, variously banded or plain monocolored; nuclear whorls three, moderately 

 large, planorboid, slightly slantingly immersed; post-nuclear whorls rounded to flattened, contracted 

 at base and strongly shouldered at the summit, traversed by eighteen to twenty-eight strong axial 

 ribs, which are excurved and usually somewhat thickened, and connected at their summits, which 

 appear beaded; these ribs extend feebly over the rounded base of the last whorl; the entire shell is 

 crossed by spiral lines, ten to sixteen or more of which appear on the exposed portion of the whorls, 

 and more, closer placed, wavy ones on the base of the last whorl; the suture is deep, subchanneled 

 and wavy; aperture ovate, produced at base; outer lip thin, meeting the oblique, slightly curved and 

 revolute columella in a broad curve; a faint callus connects the posterior angle of the ap^erture with 

 the insertion of the columella. 



Dimensions. — Long. 6.5 mm.; diam. 1.9 mm. 



The specimen figured is from the Todos Santos Bay, Lower California, and 

 has nine post-nuclear whorls. One of the same number of whorls from San Pedro 

 measures: long. 6.2 mm; diam. 1.7 mm. 



Recent specimens in our collection range from Monterey to Todos Santos 

 Bay, Lower California. The species occurs also in the post-Pliocene beds at San 

 Diesro and San Pedro. 



--t)^ 



294. Turbonilla (Pyrgiscus) crebrifilata Carpenter. 



Plate II, Figs. 6 and 6(x. 



Chemnitzia crebrifilata CpR., Ann. Mag. Nat. Hist., 3d Ser., Vol. XV, 1865, p. 395. 



Shell milk white to waxy yellow to yellowish brown in color, and of similar shape to 

 T. tenuiaila Gld. ; nuclear whorls three, helicoid, slantingly one-third immersed; extending a little 

 beyond the outline of the spire on one side; post-nuclear whorls at first well rounded, later flattened, 

 strongly shouldered at the summit and ornamented by eighteen to twenty-four very pronounced, acute 

 and somewhat flexuous, irregularly slanting axial ribs, which are outcurved at the summit of the 

 whorl and there held in union by a spiral thickening of the wavy shoulder; intercostal spaces moder- 

 ately deep and very broad, at least double the width of the ribs, with a quite deep depression immedi- 

 ately below the shoulder, which causes the summits of the whorls to appear crenulate, and 

 ornamented by about eight to ten spiral striations of varied width and spacing; these striations 

 frequently extend over the ribs and cause the intermediate ground to appear as raised ridges; suture 

 deep and wavy; periphery and base of the last whorl well rounded, the axial ribs extending faintly 

 over the base to the umbilical region; the base is marked by spiral striations similar to those of the 

 exposed portion of the whorls, but here they are more wavy and adjacent; aperture ovate, rather 

 large, acute posterior angle, and the base somewhat produced; outer lip thin, meeting the oblique, 

 somewhat twisted and revolute columella in a gentle curve; a faint callus extends from the posterior 

 angle of the aperture to the pillar. By transmitted light a broad, white, revolving band becomes 

 apparent in the peripheral region of the aperture in dark-colored specimens. 



Dime7isions. — Long. 5.4 mm.; diam. 1.6 mm. 



