MAZATLAN UNIVALVES 415 
spiraliter striatis, supra levibus ; apertura ovali, peritremate 
ma continuo, plica subdistinctd. 
This species is known by the deeply cut channel above the 
suture, and the transverse bars continued on the other side of 
the channel in the form of fine lines running round to the 
minute umbilicus, with the interstices minutely spirally striated. 
The inner lip is seen best in dead specimens. The labrum is 
indented by the channel. The number of transverse ribs is 
variable. Long. °042, long. spir. 024, lat. °023, div. 25°. 
Hab.—Mazatlan ; 7 sp. off Spondylus; L’pood Col. 
Tablet 1964 contains the largest speciiiien. 
Section B. Sheil strong, short, spirally ribbed or nodulous. 
500. PaRTHENIA ARMATA, 7%. 8. 
P. t. ovato-conicd, solida, alba; vertice nucleoso planato sub- 
tumente, anfr. ii., subprominente, verticaliter sito, marginibus 
spire excurvatis vie superante ; anfr. v. normalibus, quarum 
prima lirulis transversis et cingulo basali, altere seriebus 
duabus spiralibus tuberculorum, et carinis duabus acutis in- 
structe ; tuberculis maxime validis xv.—xx., serie swperiore 
claviformibus, inferiore subquadratis, in adulta aperturam 
versus compressis, pene evanidis ; carind und majore in peri- 
pherid, alterd in basin, parietem plicante; plicé columellart 
inferiori ; apertura ovata ; labro tenut ; suturis tmpressis. 
This beautiful and highly sculptured species is somewhat 
analogous to O. gemmulosa, C. B. Ad. Cont. Conch. no. 7, 
p- 109, from Jamaica; from which it differs in the number and 
strength of the tuberculous ridges. The principal keel falls 
into the suture of the succeeding whirl. The tubercles are not 
parallel, being more numerous in the lower row. In the con- 
traction of the lower whirl and thinness of the outer lip, it 
resembles Chrysallida. Long. *1, long. spir. ‘076, lat. ‘034, 
div. 28°. 
Hab.—Mazatlan ; 12 sp. off Chama and Spondylus ; Z’pool Col, 
Tablet 1965 contains the most perfect specimen. 
501. PaRTHENIA EXARATA, 2. S. 
P. t. conicd, valida, parva, alba ; vertice nucleoso minuto, in 
parte truncata celato; marginibus spire subrectis; anf. iv. 
profundississime exaratis, carinis i. obtusioribus, validissimis 
