244 MAZATLAN UNIVALVES 



umbilicum et inter carinas centrales evanidis ; aperturd a 

 carinis angulatd, inter duas carinas anfr. penult, attingente ; 

 anfr. ult. plus minusve decumbente. 

 Pan. Shells, no. 259, pp. 184, 315. 



Having written the above description (under the name of 

 V. trigonata), a minute examination of the type specimens in 

 Mr. Cuming's collection proves them to be identical with the 

 Panama shell. It is remarkable that Prof. Adams has not 

 mentioned the stout keel above the periphery, nor the crowded 

 spiral striae over the surface, which however are clearly marked 

 on his specimens. If there are similar omissions in other 

 diagnoses, it may be that some of the other species have been 

 before described. The typical markings are with transverse 

 riblets, about 20 to the whirl, on the outer half of the base, and 

 between the keels on the spire : but in one specimen are nearly 

 double that number. The spiral striae are over the whole 

 surface. The keels are sharp, smooth, and extremely promin- 

 ent. It is difficult to estimate the divergence, as it depends 

 on the depression of the last whirl, which in one of the adult 

 specimens makes the angle 150, in the other 170. Long. '025, 

 lat. '06 by '05. 

 Hob. Panama ; 7 sp. in sand ; C. JB. Adams. Mazatlan ; 2 



adult and 4 young sp. off Spondylus and Chama ; L'pool Col. 



Tablet 1156 contains the most characteristic specimen. 



306. VlTBINELLA COEONATA, n. S. 



V. t. " V. exiguce" simili, sed discoidea, striis spiralibus nisi 

 in umbilicum nullis, seu evanescentibus ; basi prope umbilico 

 valde angulato ; carind media maxime extante ; rugis radianti- 

 bus, injuniore valde extantibus, intus carinam basalem, et supra 

 spiram, carinam posteriorem in spird superantibus, quasi coron- 

 antibus. 



The distinguishing radiating rugae which cross the keel on 

 the spire and give it a serrated or coronated appearance are 

 very conspicuous on the young shell ; but, alolig with those 

 on the base, they become evanescent as the shell arrives at 

 maturity. The species is further distinguished from Y. ex- 

 igua by the absence of spiral striae except in the umbilicus ; 

 and from both this and V. tricarinata by its extremely depress- 

 ed growth, the upper keel completely hiding the spire. Only 

 one perfect and 3 imperfect specimens were found. Long. '02, 

 lat. '055 by '045, div. 185. 



