THE SESSILE BARNACLES. 29 



very narrow; the outer face is less convex, and the plate is not 

 twisted toward the apex. The movable tergum is lengthened in 

 the direction of the diagonal rib, and its articular ribs are unevenly 

 spaced. The recurved beaks of the fixed scutum and tergum are 

 very long. Rostrum and carina interlock by two very large and 

 one small tooth in the rostrum, one very large and two or three 

 small teeth in the carina. There are some very minute, granose ribs 

 above the upper articulating rib of the rostrum, none above that of 

 the carina. The rostrum is the largest and highest plate. It extends 

 around the end of the barnacle, as in V. alba. Basal margin of the 

 wall is obtuse. Greatest carinorostral length 3.9 mm.; height of 

 fixed terguni 1 mm. 



Three individuals on one spine agree in size and the other features 

 mentioned above, except that one has the fixed tergum lower. 



While this and the preceding forms are described as subspecies of 

 V. alba of the Gulf Stream, it is not to be supposed that they are 

 derivatives of the Floridian form. The direction of the oceanic cur- 

 rents leads us to conclude that the Caribbean forms represent a 

 southern stock which was also carried northward, where the form 

 described as typical V. alba arose. 



GROUP OP V. NEXA. 



Basal borders of the sub vertical wall-plates either inflexed or 

 simple. Fixed scutum, without a distinct myophore, though there is 

 an adductor pit. The apex of the rostrum is removed from the upper 

 edge of the plate. Sculpture strong. 



A group of small, elaborately sculptured forms, distinguished as 

 follows : 



a 1 . Basal borders of the wall inflexed in the adult stage, West Indies. . V. nexa Darwin. 

 a 2 . Basal borders of the wall not inflexed. 



6 1 . Movable scutum and tergum each with 4 articular ribs, Andaman 



Islands V. koehleri Gruvel. 



6 2 . Movable scutum and tergum each with 3 articular ribs, Philippines. 



V. intexta Pilsbry. 

 VERRUCA NEXA Darwin. 



Plate 3, figs. 1, la, 16, Ic. 



1854. Verruca nexa DARWIN, Monograph of the Cirri pedia, Balanidse and Verru- 

 cidae, p. 522, pi. 21, figs. 5. 



Type. British Museum. 



Type-locality. West Indies, on a gorgonian. 



Distribution. Albatross station 2324, off Havana, Cuba, in 33 

 fathoms. 



The barnacle l is oblong, boxliko, with subvertical side walls and 

 flattened top, the movable plates parallel to the plane of the base. 2 



1 The specimens have now faded nearly to white, but were reddish when I first saw them in 1906. 



2 Tro'essor ru vel has placed V. ncia in the group having the plane of the movable plates perpendicular 

 to the base, and in his monograph speaks of it (p. 179) as non dcprimee;" also "scutum fixe sans aucune 

 depression pour 1'adducteur." Those terms certainly are not applicable to V.ncia. I do not know what 

 species was in view. 



