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, n. s. 



O.t. " 0. vallata" simili, sed angustiore ; vertice nucleoso 

 subtumente, anfr. primo norrnali rotundato ; carinuld nulld ; 

 ? plica celatd. 



The plait does not appear in the only specimen found. It is 

 probable however, from its great resemblance to O. vallata, 

 that it exists within. Long. '045, long. spir. '024, lat. '027, 

 div. 22. 



Hab. Mazatlan ; 1 sp. off Chama ; L'pool Col. 

 Tablet 1957 contains the specimen. 



493. ODOSTOMIA TENTHS, n. s. 



O. t. tenui, subconicd, alba ; vertice nucleoso parvo, decliviter 

 iminerso ; anfr, iii. normalibus, subplanatis, suturd impressd ; 

 peripherid haud angulatd, basi rotnndatd, umbilico conspicuo ; 

 aperturd obovali, peritremati continuo, acuto ; labro canali 

 suturali apariete disjuncto ; callositate parvd in labio columel- 

 lari 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 stitural canal, 

 which is formed by the separation of the last whirl, not the 

 grooving of the parietal. Long. '064, long. spir. '038, lat. '028, 

 div. 22. 



Hab. Mazatlan ; 2 sp. off Spondylus : Lpool Col. 

 Tablet 1958 contains the largest specimen. 



