MAZATLAN UNIVALVES 423 



Jf 511. CHEYSALLIDA FASCIATA, n. s. 



CJir. t. parvd, avoided, alba ; vertice nucleoso parvo, declivi, 

 omnino celato ; marginibus spires excurvatis ; anfr. normalibus 

 iv. v., clatJiris circiter xviii. tuberculosis, lirulis iii. plus 

 minusve conspicuis, decussantibus, cingulo quoque super suturam 

 extante, interstitiis utrinque tenue decussatis, ornatd ; basi 

 rotundatd lirulis circiter iv. spiralibus subacutis cinctd, inter- 

 stitiis latis, lineis clathra continuantibus tenue decussatis ; plied 

 columellari celatd, parvd, obtusd ; peritremati vix continue, 

 labio tenui. 



This species has some characters in common with Chr. mar- 

 ginata, C. S. Ad. (Pan. Shells, no. 226) from which the number 

 of ribs at once distinguishes it. In many respects it resembles 

 Chr. ovulum, from which it differs in its breadth and larger size, 

 in the prominence of the suprasutural band, the fineness of the 

 few basal striae, and the sunken position of the nuclear whirls 

 on the broadly truncated ('01 across) spire. Some of the 

 specimens are short and broad in proportion, which is the 

 character of the earlier stage generally. A young shell, with 

 two and a half normal turns, measures long. '036, long. spir. 

 017, lat. '027, div. 30. The largest, unusually elongate, yet 

 not quite mature, long. '083, long. spir. '046, lat. '042, div. 23. 

 Sab. Mazatlan ; 20 sp. off Spondylus ; L'pool Col. 



Tablet 1981 contains 5 specimens ; two very young, one 

 dwarf, one mature, broad, and one almost mature, elongated. 



512. CHETSALLIDA OVULUM, n. s. 



Chr. t. minima, gibbosd, albd, solidiore ; vertice nucleoso 

 "Chr. communi" simulante, marginibus spirce valde excurvatis, 

 haud superante ; anfr. normalibus iii. et dimidio, interdum 

 clathrulis transversis circiter xviii., interdum lirulis spiralibus 

 iv. nodulosis superantibus ; lacuna suturali profundd, in basin 

 rotundatam, effusam, haud continud ; aperturd compactd, labro 

 parum tenui, intus solido ; plied columellari obtuso ; lirulis 

 rotundatis in basin spiralibus circiter vi., interstitiis minimis, 

 vix decussatis. 



About 70 specimens of this stumpy little species were found, 

 differing from the dwarf forms of Chr. communis in the strength 

 of the spiral riblets, which generally break the transverse 

 bars into coarse tubercles, and in the small number and promi- 

 nence of the rounded basal striae. The whirls are very few, 



