MAZATLAN UNIVALVES 419 



minimis, guarum una suprasuturalis simplex, et iv. tuberculoses, 

 tuberculis rotundatis, lineis transversis sibi parallelis sitis, in 

 anfr. penult, circiter xx., in t. adult d evanidis ; lirulis in basin 

 rotundatam circiter vii., t. junior e acutioribus, inter stitiis tennis- 

 sime et creberrime decussatis ; aperturd ovatd, peritremati vix 

 continue ; labro acuto, vix planato, supra suturam producto, ad 

 basin vix sinuato ; labio in parietem tenuissimo, infra distincto, 

 rimulam umbilicalem formante ; plica intus acutd, extus obtusd, 

 haud conspicud. 



This fine species approaches Monoptygma. It differs from 

 Chr. rotundata in the tuberculation of the spiral ribs and the 

 much greater prolongation of the shell. The basal strise seem 

 to become broader in the adult, as the tuberculation of the 

 upper ribs vanishes. The young shells are slender, with 

 rounded bases. The tubercles are arranged in the form of 

 transverse ribs, .parallel to each other, and running in slanting 

 lines to the apex. Long. '153, long. spir. '095, lat. '067, 

 div. 22. 



Hab Mazatlan ; 4 sp. and fragment, off Spondylus ; L'pool 

 Col. 



Tablet 1971 contains the largest sp. presented by E. D. Dar- 

 bishire, Esq. and a very young shell which may belong to this 

 species. 



SECTION B. Species typic.a. 



507. CHRYSALLIDA COMMUNIS, C. JB. Ad. 



Chemnitzia communis, C. B, Ad. Pan. Shells, no. 223, pp. 166, 



312. 



Chr. t. ovato-oblongd, gibbosd, solidiore, nitente, albd ; vertice 

 nucleoso parvo, spires truncationem dimidio tegente, anfr. ii. 

 verticaliter sitis, apice vix celato ; marginibus spires maxime 

 excurvatis ; anfr. normalibus iv. vi, planatis, suturd profundd ; 

 clathris transversis, utringue marginibus spir a parallelis, testd 

 juniore conspicuis, aperturam versus evanescentibus, juxta 

 peripheriam terminantibus, anfr. penult, circiter xxii. ; liris 

 tpiralibus iv. vel v. suprasuturaUbus, anfr. primis minoribus, 

 anfr. ultimis scepe clathras in tubercula vcantibus ; lirulis 

 rotundatis vix expressis circiter x. supra basin ovatam inter- 

 stitiis punctulis decussatis ; aculpturd in labro tenuissimo, dia~ 

 phano evanescente ; labro antice late sinuato, postice planato 

 angustato, ad suturam constricto, labio sape a pariete separato ^ 



