No. 1610. NEW PACIFIC COAST MOLLUSKS—DALL. = Yi 
whorls which become more and more rounded and constricted in 
front of the suture; suture distinct, with (on the last whorl 20) 
small milk-white points coronating it and separated by small pits 
corresponding to the interspaces between the ribs; whorls smooth, 
or with obsolete indications of arcuate ribs which show by their 
more opaque whiteness faintly against the translucent under layer; 
basal disk hardly perceptible, not angulating the whorl, but trace- 
able by the row of faint indentations which bound the obsolete 
marein; surface originally covered with a microscopic reticulation 
of revolving and vertical lines impressed on a very thin chalky 
layer; base produced; aperture simple, surrounded by a thick white 
callous margin, the opening obovate. Height of shell, 12; of last 
whorl, 6; of peritreme, 3.5; maximum diameter, 4.0 mm. 
Type—Cat. No. 168669, U.S.N.M. Mazatlan, Mexico. | 
The type-specimen is somewhat worn and polished, but shows the 
minute sculpture in sheltered places. 
OPALIA (DENTISCALA) MEXICANA, new species. 
Shell small, slender, white, opaque, with two nuclear smooth 
whorls and seven subsequent whorls; nucleus very small, blunt; 
subsequent whorls moderately rounded; suture distinct, with nine 
coronating points separated by deep and conspicuous pits; the ribs 
corresponding to the points are wide and thick but obsolete on the 
periphery, appearing again near the margin of the basal disk, where 
they are separated by shallow but distinct depressions; surface 
microscopically sculptured by sharp revolving lines reticulated by 
somewhat fainter incremental lines; basal disk shghtly flattened, 
its periphery slightly angulating the whorl; aperture nearly circu- 
lar, surrounded by a thick, shghtly reflected peritreme. Height of 
shell, 11; of last whorl, 5; of peritreme, 2.7; maximum didmeter, 
4.0 mm. 
Type.—Cat. No. 59336, U.S.N.M. Acapulco, Mexico; W. H. Dall. 
This is easily distinguished from the preceding by the smaller 
number and greater strength of the ribs. O. mazatlanica is more 
like O. hotessieriana Orbigny, of the West Indies than any other 
west American species known to me. 
Genus EPITONIUM Bolten. 
(Scalaria Lamarck. ) 
EPITONIUM (CRISPOSCALA) ACROSTEPHANUS, new species. 
Shell slender, acute, turrited, with two nuclear and nine or more 
subsequent whorls which are in contact, though separated by a deep 
suture across which the varices are continuous; axial sculpture of 
(on the last whorl 14) nearly vertical, thin, sharp, slightly re- 
flected varices, which are expanded near the suture into a smull 
