244 MAZATIAN UNIVALVES 



umbilicum et inter carinas centrales evanidis ; aperturd a 

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

 amfr. ult. plus minusve decumhente. 

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



Having written tlie 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 strife over the siu'face, 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 tji)ical 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 strise 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 whii'l, which in one of the adult 

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

 lat. -06 by -05. 



Hah. — Panama ; 7 sp. in sand ; C. B. Adams. — Mazatlan ; 2 

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

 Tablet 1156 contains the most characteristic specimen. 



306. VlTEINELLACOEONATA, M. *. 



V. t. " V. exigwce" simili, sed discoided, striis spiralihus nisi 

 in umbilicum nullis, seu evanescentibus ; basi prope umbilico 

 valde angulato ; carina media maanme extante ; rugis radi anti- 

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

 .<ipiram, carinam posteriorem in spird superantibus, quasi coron- 

 antibus. 



The distinguishing radiating rugse which cross the keel on 

 the spire and give it a serrated or coronated appearance are 

 very conspicuous on the yoimg shell ; but, along with those 

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

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

 igua by the absence of spiral stria) except in the umbdiciis ; 

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

 ed growth, the upper keel completclj- hiding the spire. Only 

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

 lat. 055 by '045, die. 185°. 



