418 MAZATLAN UNIVALVES 



Of this broad and strongly built species, three young shells, 

 one adolescent and one adult were found. It is known at once 

 from Chr. ovata by the prominent little vertex at the head of 

 the pointed spire. The first whirls are very spreading. The 

 base is angulated in the adolescent shell, but rounded in the 

 adult. The base of the columella is produced in all stages, 

 almost notched when young. The labrum is extremely thick 

 in the broken shell. The sutural groove is formed as in Chr. 

 telescopium, but the sculpture most resembles that of Chr. 

 ovata. A. young specimen with two and a half normal whirls 

 measures long. '046, long. spir. '022, lat. '034, div. 50. 



The adult sp. '163, '098, '072, 30. 

 Sab. Mazatlan ; 5 sp. off Spondylus ; Lpool Col. 

 Tablet 1969 contains the adult and a young specimen. 



505. CHEYSALLIDA EOTUNDATA, n. s. 



Chr. t. tenuiore, ovata, solidd; vertice nucleosoparvo,planato, 

 verticaliter in medio sitce, prominente, marqinibus spirce excur- 

 vatis parum superante ; anfr. iv. normalibus, tumentibus, 

 suturis conspicuis liris xi. spiralibus, solidis, rotundatis, con- 

 tiguis, guarum v. in spird sitce sunt ; interdum, maxime in testa 

 juniore, transversim tuberculosis ; interstitiis tenue decussatis ; 

 basi rotundatd; aperturd parum contractd, peritremati continuo, 

 labio tenui, plied obtusd, vix celatd. 



Of the shape of Chr. ovata, but even more like the normal 

 Odostomise ; with a very different vertex ; and separated from 

 all the other species by the transverse markings being almost 

 obsolete. They appear however here and there, as though to 

 shew the bond of relation. In this species also the young 

 follows the type of the adult. Nine complete shells and a few 

 fragments were found. Long. '09, long, spir* '048, lat. '045, 

 div. 35. 

 JIab. Mazatlan ; very rare, off Spondylus ; L'pool Col. 



Tablet 1970 contains the youngest, the largest *and an inter- 

 mediate specimen. 



506. CHEYSALLIDA OBLONGA, n. s. 



Chr. testa ovato-oUongd, tenuiore, alba ; vertice nucleoso ut 

 in " Chr. rotundatd ; " anfr. v. normalibus, subconvexis, suturd 

 distinct a ; liris v. in spird spiralibus, rotundatis, interstitiis 



