20 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



freezing point (3 to 4 C.), may have a general distribution over the 

 floor of the Atlantic, where the uniformity of conditions in the dark, 

 cold, deeps opposed no barriers to their distribution. These abyssal, 

 cold-water species have a characteristic erect shape not found in any 

 Verruca from shallow or warm water. 



A certain correlation therefore exists between the shape of the 

 barnacle and its habitat. The shallow-water species, V. stromia, V. 

 spengleri, and V. Isevigata, are all much depressed, having broadly 

 spreading walls, while all of the high species with erect movable 

 plates live in very deep or very cold water. There are also in inter- 

 mediate depths and temperatures numerous boxlike forms with steep 

 walls and flattened top. 



I have given somewhat detailed accounts of several species, such 

 as F. alba, since very little is known of the range of variation in 

 Verruca, nearly all the species except V. stromia and V. Isevigata 

 being known from one or very few individuals, from a single station. 

 The series of numerous examples from several stations before me for 

 the first time allows some estimate of the kind and degree of varia- 

 tion among individuals and colonies of the deep-water forms. It 

 appears that, as Darwin has noticed in Balanus, the individuals of 

 a colony usually resemble one another rather closely. Different col- 

 onies of one species may sometimes show rather marked differences, 

 even in the same district, while in others, widely separated, the 

 specimens may be practically identical. It should be noted that 

 the widely separated colonies recorded herein in which the individ- 

 uals are very similar, occur along the course of the Gulf Stream, such 

 as the colonies of typical F. alba in Florida Strait and off Hatteras. 

 The wandering nauplii are doubtless borne northward in a constant 

 stream upon this mighty current. 



KEY TO VERRUCA OP THE WESTERN ATLANTIC AND CARIBBEAN ZOOLOGICAL PROVINCES. 



a 1 . Movable plates sloping steeply or nearly erect; parietes of fixed scutum and ter- 

 gum separated by a large radio-alar area; basal edges of wall not inflexed. 



6 1 . Apical cavities of fixed tergum and rostrum partitioned off; a partition-like 



myophore in fixed scutum V. euglypta, p. 39. 



6 2 . Cavity simple, without partitions, myophore, or distinct adductor pit; fixed 



tergum with narrow paries. 

 c 1 . Movable scutum and tergum each with one articular rib; no distinct rostro- 



carinal articular teeth or ribs; size small V. hoeki, p. 41. 



c 2 . Movable scutum with one or two, tergum with one distinct and two very weak 

 articular ribs; rostrocarinal suture serrate; greatest diameter and height 

 about equal. 



t/ 1 . Rostrum with 4, carina 5 subequal articular ribs V. bicornula, p. 43. 



(P. Rostrum and carina each with 2 distinct and one imperfect rib. 



V. rathbuniana, p. 41. 

 C 3 . Similar to c 2 , but height decidedly less than greatest diameter. 



V. darwini, p. 45. 



