AFFINITIES OF THE PELAGIC TUNICATES— BROOKS. 155 



In the species that is here described the outer surface of the test is smooth in young colonies, 

 and the mouths are at the bottoms of conical pits, figure 2, as they are in some of the zooids of 

 old colonies. Most of the zooids of older colonies have processes that are conical and symmetrical, 

 and the mouths are terminal, figure 8. There is nothing distinctive in the length of the processes, 

 for some are short and some long. While they are usually conical and symmetrical with reference 

 to the long axis of the aseidiozooid, they are sometimes elongated on the side that is dorsal to the 

 mouth, winch is thus oblique and on the ventral side of the process at some distance from its tip. 



DipL Ural symmetry. — The dipleural symmetry that characterizes this species is recognizable 

 in the embryo, becoming more marked with the growth of the colony. 



The embryonic colony of four primary ascidiozooids, figure 1, is nearly circular, although the 

 two ascidiozooids. pa 1, that are to occupy the sides of the colony, are easy to distinguish from 

 the two. jut 2, that are to lie on the edges. 



The young colony, with seventy ascidiozooids shown in side view in figure 2 and in transverse 

 section in figure ?>, exhibits marked dipleuralism. 



There are seven ascidiozooids on each edge, or fourteen in all, and twenty-seven on each side, 

 or fifty-four in all, and the four primary ascidiozooids, pa 1 and/A/ 2, are readily distinguishable. 

 The diagrammatic section, figure 3, is through the verticil that is fourth from the closed end 

 in figure 2. As the diagram shows, there is one zooid on each edge at this level, and there are 

 five on each side, or twelve in all, and the thickness of the colony is about equal to one-half its 

 breadth, so that the ratio of thickness to breadth is one-half. 



In the adult colony, shown in side view in figure -t, in end view in figure 6. in edge view in 

 figure 5. and in section in figure 7, there are about sixty zooids in each cross section, and the 

 thickness of the colony is to its breadth about one to four. 



VertidUation. — In the full-grown colony there is no visible trace of an arrangement of the 

 zooids in rings, although this arrangement is regular and conspicuous in the young colony shown 

 in figure 2. 



In this there are seven rings, with four zooids in the first, eight in the second, ten in 

 the third, twelve in the fourth, twelve in the fifth, fourteen in the sixth, and ten in the seventh, 

 or seventy in all. The regular verticillation is obliterated, in older colonies, by the interpolation 

 of new buds between the rings. 



N'JoG'.l — VOL 10—11 11 



