NO. 1574. WEST A MER ICA N P YRA Ml DEL LID. E— DA LL A ND BA R TSCH. 509 



The above is the original description by Gould. Turbonilla {Pyr- 

 giscut<) tenuicxda 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 onl}^ add to the confusion which this paper is intended to dispel. 

 The following comprehensive description will embrace, we believe, 

 all theiorms coming under this name: 



Shell slender to somewhat stubby and inflated, varjdng 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 18 to 28 strong vertical 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 incised spiral lines, 10 to 16 or more of which apjjear on the exposed por- 

 tion of the whorls, and more, clo.ser placed, wavy ones on the base of the last whorl; 

 the suture is deep, subchanneled and wavy; aperture ovate, i)roduced 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 aperture with the insertion 

 of the columella. 



Dimemsionsi. — Length ti.5 mm.; diameter 1.9 mm. 



The specimen figured is from Todos Santos Ba}^, Lower California, 

 and has 9 post-nuclear whorls. One of the same number of whorls 

 from San Pedro measures: length 6.2 mm.; diameter 1.7 mm. 



The U. S. National Museum contains the following specimens: 



Specim.ens of Turhonilla {Ryrgiscns) tenuicula Gould. 



TURBONILLA (PYRGISCUS) CASTANEA, new species. 

 Plate XLVII, flg. 7. 



Shell very large, stout and heavy, chestnut brown. Nuclear whorls 

 decollated. Post-nuclear whorls well rounded, ornamented by many 

 broad, flattened, more or less regular, and evenly placed retractive axial 

 ribs, of which about 22 appear upon the third, 26 upon the fifth, and 



