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. 

 .9pir. -032, I at. '028, div. 30". 



Ba6.— Mazatlan ; 10 sp. off Chama and Spondylus ; L'pool Col. 



Tablet 1956 contains 3 sp., one youug, translucent, another 

 adult, the third slightly distorted in growth. 



492. Odostomia mammillata, n. s. 



O. i. "0. vallate" siinili, sed angustiore ; vertice nucleoso 

 suhtumcnte, anfr. primo normali rotundato ; carinuld nulld ; 

 ?plicd celatd. 



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

 probable however, from its gi-eat resemblance to O. vallata, 

 that it exists within. Long. "Olo, long. spir. "024, lat. "027, 

 div. 22". 



JTai.— Mazatlan ; 1 sp. off Chama ; L'pool Col. 

 Tablet 1957 contains the specimen. 



493. Odostomia tenuis, n. s. 



O. t. teniii, sithconicd, alhd ; vertice nucleoso parvo, decliviter 

 immerso ; anfr. iii. normalibns, suhplanatis, suturd impressd ; 

 peripherid hand angulatd, hasi rotundatd, umhilico conspicuo ; 

 aperturd ohovali, peritremati coniinuo, acuto ; lahro canali 

 suturali a pariete 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, aud in the sutural canal, 

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

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

 div. 22". 

 JTai,— Mazatlan ; 2 sp, off Spondylus ; L'pool Col. • 



Tablet 1958 contains the largest specimen. 



