MAZATLAN UNIVALVES 417 



Section A. Species Odostomoideee. 



503. Cheysaliida ovata, n. s. 



Ckr. t. haud parva, solidd, ovatd, alhd ; vertice nucUoso 

 parvo, omnino celato ; marginihits spit'ce paruni exciirvatis ; 

 anfr., paiiciorihus quoad magnUudinem, iv. et dimidio, suhro- 

 tundatis ; suturd impressd ; liris iuherculosis transversis, testa 

 juniore suhdistantihus, testd adultd contiguis, marginihits spires 

 vix parallelis ; lirulis spiralibus, in spird iv. vix vionstrantiitis, 

 circa peripheriam et basin rotundatas vi. validis, rotundatis, 

 ifiterstitiis parvis rugoso-decussatis ; ape^^turdpai^m contractd, 

 peritremati continuo, labio interdum rimulam iimbilicaletti 

 monstrante ; plied solidd, obtusd, parum celatd. 



This species and the next are at the confines of the group, 

 with which they agree in general habit, sculpture, and con- 

 tinuous peritreme, while the form is that of the typical Odos- 

 tomiffi. The pattern closely resembles that of Chr. nodosa, 

 and the apex that of Chr. fasciata, from both of which it differs 

 in its broad expanding form, the adolescent shells being like 

 the adults. The lip is not thin, but agrees with the group in 

 being much more solid within, as is shewn by the broken 

 shells, of which there were several, though xerj few of any age 

 were perfect. The largest (a monster for the gi'oup) measures 

 long, 'loo, long. spir. '08, lat. "083, div. 35". 



.HWi.— Mazatlan ; very rare, off Spoudjdus ; L'pool Col. 



Tablet 1968 contains the youngest, the oldest, and an inter- 

 mediate specimen. 



501. Cheysallida nodosa, n. s. 



Chr. t. subconicd, solidd, alhd ; vertice nucleoso minimo, 

 prominentc, marginibiis spii'CB vix excurvatis parum superante ; 

 anfr. ■normalibus v. latis, subplanatis ; lirulis spiralibus iv. 

 transversis usque ad xvii. sibi parallelis, ad inter secti ones nodosis; 

 tuherculis rotundatis, validis, transversim attingentibus, spirali- 

 ier plerumque se])aratis ; li)'ulis transversis supra suturam 

 impressam declivibus ; lirulis spiralibus in bast rotundatd 

 V\. rotundatis, interstitiis teniie decussatis ; plied columellari 

 parum celatd, validd, obtusd ; aperturd (in t. adultd) oblongd, 

 parum contractd, ad basin productd, peritremati contintto, labio 

 hand tenui. 



