424 MAZATLAN TTNIVALVES 



sometimes not more than two and a lialf in tlie adult. A 

 ? variety has the sculpture much finer. A large sp. measures 

 long. "055, long. spir. "032, lat. "027, div. 25". 



Sah. — Mazatlan ; not common, oflf Spondylus and Chama ; 

 L'jaool Col. 



Tablet 1982 contains 9 specimens in different stages. 



Section C. Species Chemnitziformes. 



513. Cheysallida clatheattjla, C. B. Ad. 



Chemnitzia clathratida, C. B. Ad. Pan. Shells, p. 165, 311, 

 no. 222. 



This species passes into the rounded cancellated forms of 

 Chemnitzia, (Subgenus Dunkeria,) from which it is known by 

 the distinct fold ou the cohimella, and continuous peritreme. 

 The last whirl is but sbghtly contracted. It is known at 

 once from the rest of the Chrysallidse by its' very elongated 

 form and rounded whii-ls. The solitary INIazatlan specimen has 

 lost its upper portion ; but the imperfection of the aperture 

 brings to light the oblique distinct columellar plait, which 

 escaped the notice of Prof. Adams. 



Hah. — Panama ; 10 sp. in sand ; C. B. Adams. — Mazatlan ; 

 1 sp. off Chama ; L'liool Col. 



Tablet 1983 contains the specimen. 



514. Chetsallida contexa, n. s. 



Chr. t. gracili, tereii, tenui, albidd ; vertice nucleoso anfr. ii. 

 heUcoidalibus, magnis, declivibus, marginibus spirce, parum 

 excurvatis, superantibus, quarum apex in anfr. nonyiali primd 

 horizontaliter jacef , parum prominens ; anfr. normalibus v. valde 

 convexis, liris obticsis circiter xiv. radiantibus, ad suturam pro- 

 fundam S(Bpius attingentibus, circa basin evanescent ibus ; lirulis 

 spiralibus in partem anteriorem^ anfractuum, interstitia tenue 

 decussantibus, quarum iii. in spirci videntur, circa basin satis 

 rotundatam 2}li'>'es ; aperturd subovali, partem contractd ; 

 columellA oblique plicata ; labio tenui. 



This remarkable shell has the apex and growth of a Chem- 

 nitzia, the convex whirls of Aclis, with the spiral plait and 

 (slightly contracted) aperture of Chrysallida. The lower half 



