30 BULLETIN 03, UNITED STATES NATIONAL MUSEUM. 



Wall-plates broadly iiifiexed at the base. Apices of the fixed scutum 

 and tergum produced and recurved. 



Movable scutum havuig three strong articular ribs and two other 

 ribs reaching the rostral margin. Inside it is somewhat excavated 

 near the apex. 



Movable tergum having three broad articular ribs, the rest of the 

 plate transversely grooved. 



The fixed scutum is radially ribbed, the ribs on the rostral side 

 interlocking with those of the rostrum. The sutural margin on the 

 tergal side has four short ribs. Inside there is a low, transverse, 

 adductor ridge, a rounded hollow above it. 



Fixed tergum ribbed, contracted above the middle, with short 

 sutural ribs on both sides. 



Carina small, with vertically ribbed paries and about seven ribs 

 which interlock with those of the rostrum, the intervals crenulate. 



Rostrum somewhat pateUifomi, the aj^px heing removed from tlie 

 margin. Carinal and scutal margms are profusely ribbed radially, 

 paries irregularly ribbed vertically. 



Carinorostral length, 4.7 mm.; height of fixed tergum, 2.1 mm. 

 The largest specimen of the t^'pe lot is said by Darwin to measure 

 0.2 inch (5 mm.) in greatest diameter. 



According to Darwin the rami of cirrus i are subequal, of 11 and 

 12 segments. In cirrus ii the shorter ramus is two-thirds as long as 

 the longer, segments 10 and 15. In cirrus iii the rami are very nearly 

 equal. The caudal appendages are very long, as in F. stromia. 



In yoimg individuals the internal ledge of the base is wantmg. In 

 one example there are tliree longitudinal ribs on the movable scutum 

 in addition to the three articular ribs; the apex of the rostrum is 

 much nearer the upper edge than in the specimen figured, though 

 still removed from it. The short articular ribs m the suture of fixed 

 scutum and tergum are wantmg; the articular ribs of rostrum and 

 carina are fewer, four in each, and more widely spaced; their inter- 

 vals smooth. The range of variation in the species is therefore 

 considerable. 



By having the apex of the rostrum well removed from the upper 

 margin of the plate, this species differs from all other Atlantic species, 

 and resembles V. intexta Pilsbry and V. koehleri Gruvel. 



Group op V. calotheca. 



Boxhke forms with strong sculpture, vertical or moderately sloping 

 walls, their basal edges not iaflexed ; fixed scutum havmg an adductor 

 pit and often an adductor ridge or myophore; apex of the rostrum 

 nearly or quite marginal. Rami of cirri i and ii subequal, or the 

 anterior decidedly over half as long as the posterior; rami of cirri iii 

 to vi nearly equal. Terminal appendages short or moderately long. 



