412” MAZATLAN UNIVALVES 
marked umbilicus, continuous and very thin peritreme, and for 
the vallum, consisting of a little ditch and mound at the 
suture, which are carried round the base. Long. ‘055, long. 
spir. ‘032, lat. °028, div. 30°. 
Hab.—Mazatlan ; 10 sp. off Chama and Spondylus; L’pool Col. 
Tablet 1956 contains 3 sp., one young, translucent, another 
adult, the third slightly distorted in growth. 
492. ODOSTOMIA MAMMILLATA, 1. 8. 
0. t. “O. vallate” simili, sed angustiore; vertice nucleoso 
subtumente, anfr. primo normali rotundato; carinulad nulla ; 
?plica celata. 
The plait does not appear in the only specimen found. It is 
probable however, from its great resemblance to OQ. vallata, 
that it exists within. Zong. ‘045, long. spir. ‘024, lat. ‘027, 
div. 22°. 
Hab.—Mazatlan ; 1 sp. off Chama; LZ’pool Col. 
Tablet 1957 contains the specimen. 
493. ODOSTOMIA TENUIS, %. 5. 
O. t. tenui, subconicd, alba ; vertice nucleoso parvo, decliviter 
immerso ; anfr, i. normalibus, subplanatis, sutura impr essd ; 
peripheri id haud angulatd, basi rotundatd, umbilico conspicuo ; 
apertura obovali, peritremati continuo, acuto ; labro canale 
suturali a pariete disjuncto ; callositate parDe in labio columel- 
lart vix conspicuo. 
Like O. vallata in the thin continuous peritreme, umbilicus, 
and slight callosity ; differing from the neighbouring species 
in its rounded periphery and base, and in the sutural canal, 
which is formed by the separation of the last whirl, not the 
grooving ofthe parietal. Long. °064, long. spir. °038, lat. *028, 
div. 22°. 
Hab.—Mazatlan ; 2 sp. off Spondylus; LZ’pool Col. 
Tablet 1958 contains the largest specimen. 
