MUSEUM OF COMPARATIVE ZOOLOGY. 107 



indicated by a groove on the interior surface ; the sculpture in young shells 

 consists of rounded granules between and irregularly over the costse and small 

 conical rough-surfaced spines arranged on the summits of the costse, but these 

 are usually rubbed down in adult specimens, after which the costae (about fifty 

 in number) and the secondary granulations become more evident ; lunule small, 

 slightly impressed, with a comparatively smooth surface, the portion pertain- 

 ing to the right valve (as usual in the genus) being about half the size of that 

 forming part of the left valve, which latter (also as usual) is produced beyond 

 the general plane of the margin, simulating a tooth ; beaks not very promi- 

 nent, not coiled as in the typical species ; inner margin irregularly grooved, 

 not denticulate ; in the left valve the wedge-shaped groove for the (wholly in- 

 ternal) ligament is separated by a projecting septum from the fossette for the 

 right cardinal tooth ; except this septum be so considered, there are no teeth in 

 the left valve ; right valve with a strong, stout, slightly anteriorly projecting 

 tooth fitting into the fossette in the left valve and immediately under the 

 beak ; the base of this tooth is supported by two buttresses, one with a con- 

 cave surface extending forward under the lunule, the other opposite, shorter, 

 and terminating under the cardinal margin, between which and its upper sur- 

 face the ligament is inserted ; a little way within the posterior cardinal margin, 

 and in general parallel with it, is a long slender tooth or lamina, which be- 

 comes obsolete in aged shells ; beside the ordinary marks of the adductor mus- 

 cles as usually described, there are two smaller but very evident muscular 

 scars, the pedal below the lunular buttress and the cardinal in the cavity of the 

 beak. Lon. 13.25 ; alt. 10.1 ; max. diam. 8.0 mm., in an adolescent speci- 

 men ; one old valve measuring in lon. 30.0, alt. 23.0, and diam. 13.0 mm. 

 approximately. 



Station 16, 292 fms. ; Lat. 23° T and Lon. 82° 43' 30" W., in 75G fathoms. 



This elegant shell has quite a different aspect from the other Vertica 

 and, misled by the the erroneous diagnosis in all the text-books, I referred it 

 to a new group in my preliminary report, reserving a description until this 

 conjecture could be verified by comparison and study. Now it seems to me 

 that the characters are insufficient to justify its separation. The above de- 

 scription of the teeth is appropriate to all the recent species I have seen, or 

 which have been well figured, except that in most of the species the cardinal 

 tooth points upward or backward, and the posterior lamina is obsolete in some 

 individuals of each species. It is by far the largest of the group, and only 

 detached valves have been noted as yet. 



Lyonsia bulla n. s. 



Lyonsia bulla Dall, Bull., loc. cit., 1878. (Not described.) 



Shell delicate, iridescent, very thin, rounded, inflated; sub-equivalve, but 

 slightly produced and gaping behind ; surface covered with a delicate evanes- 

 cent epidermis, which is raised into very tine short beards in radiating lines 

 from the umbones ; these on the posterior third of the shell form rather dis- 





