240 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



greatly with individuals. This is apparent in smaller colonies as 

 well. For example, the dimensions of certain of our specimens are 

 as follows: Length, 8 cm., thickness at open end, 1.8 cm., at closed 

 end, 1.1 cm.; length, 7.5 cm., thickness at open end, 1.5 cm., at 

 closed end. 1.2 cm.; length, 10 cm., thickness at open end, 2.3 cm., 

 at closed end, 1.5 cm.; length, 3.1 cm., greatest thickness, at open 

 end, 0.9 cm.; etc. As already stated, some few individuals are 

 thickest in the middle, some are almost uniformly cylindrical, but 

 the majority are distinctly conical, that is, they taper toward the 

 closed end (fig. 45, pi. 34). 



The test is fairly rigid, retaining well the form of the colonial tube 

 in preserved specimens. It is ordinarily colorless and transparent, 

 but varies through pale yellowish to a distinct pinkish flesh-color. 

 The color of the test may perhaps, as Herdman (1888) believes, be 

 derived from the masses of pigment cells lying on the esophagus, 

 intestine, and testis of the zooid, though how they influence the color 

 of the test is not clear. That these pigment cells may be the source 

 of the test color is suggested by the fact that the colors of the two are 

 about the same except for intensity, and that in the form giganteum, 

 as described by Herdman, the inner zone of the test lying above these 

 pigmented organs is deeper in shade than the outer layers. No 

 specimens of the subspecies atlanticum have been reported in which 

 there is any trace of blue or greenish color. 



Characteristic of this whole group of forms is the presence of, and 

 especially the shape of, the test processes (fig. 30, pi. 26). These are 

 most characteristic as observed in rather young colonies (fig. 53, pi. 

 36). Here they arise each in connection with a zooid. The process 

 itself is a broad, obliquely truncated cone, the truncated surface of 

 which faces slightly toward the closed end of the colony, i. e., in the 

 same direction as do the ventral sides of the zooids. Upon this trun- 

 cated area the oral aperture of a zooid is situated so that the mouth 

 thus appears to open obliquely ventrally (fig. 30). In many younger 

 zooids of this type form (fig. 32) and occasionally in older zooids of 

 some of the other subspecies (fig. 36, pi. 29), this truncated area is de- 

 pressed, forming more or less of a funnel leading to the mouth. In this 

 particular form (P. atlanticum atlanticum) we have, appearing rather 

 early, a characteristic denticulation along the lateral edges of the 

 truncated area of the test process, and at its dorsal tip (figs. 30 and 33). 

 This character almost serves in itself to distinguish this variety from 

 the other varieties of the species, for it is of very constant occurrence, 

 and, if at all well developed, seems to be one of the distinctive, though 

 minor features indicating this race. In older colonies, test processes 

 sometimes develop to great length, so that they give to the colony a 

 bristling, spiny appearance (fig. 45, pi. 34). The oral processes of the 

 corresponding zooids lengthen themselves proportion ately, so that 



