248 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



and California, not more accurately located; six specimens, Cat. 

 Nos. 6443 (Holotype) and 3069 (Paratypes) U.S.N.M.) It seems 

 likely that this is a geographical subspecies, whose distribution is 

 limited to the waters of the Pacific. 



PYROSOMA ATLANTICUM PARADOXUM, new subspecies. 



Plate 29, figure 35. 



Among the specimens of Pyrosoma collected in the Pacific by the 

 Albatross, was one which in general appearance closely resembled P. 

 atlanticum atlanticum. On making a study of the zooids, however, 

 certain small but distinctive differences were found. In making this 

 a subspecies, then, we describe conditions as they are found, not for 

 the purpose of multiplying varieties indefinitely, but rather to point 

 out and illustrate the great degree of divergence in this group. 



As characteristic of the colony, should be mentioned its remark- 

 able limp and gelatinous condition (formalin preservation), which is 

 exceptional in this major species; also the weak development of the 

 colonial diaphragm, and the consequent large size and irregular 

 contour of its aperture. The test-vessels running into the dia- 

 phragm appear to have degenerated completely. In other respects 

 the colony resembles that of P. atlanticum atlanticum; the test is 

 very transparent, the zooids whitish; test-processes fairly long and 

 tapering, with oblique areas of truncation which are a little denticu- 

 late on their edges. The dimensions of the colony are, length 8.6 

 cm., width, at open end 2.4 cm., at closed end 1.3 cm.; from which 

 it will be seen that the colony tapers rather strongly. There is a 

 suggestion of flattening, but this may not be natural. The zooids 

 are irregularly arranged in the test. 



But the features which most strongly characterize this subspecies 

 are found in the zooid. The mantle, and in fact all the tissues of the 

 body, are quite delicate. The branchial components are more 

 numerous than in the subspecies atlanticum: of longitudinal branchial 

 bars there are 16-17, only rarely 15; the rows of stigmata are 33-37. 

 There are about 9 dorsal languets. Other differences more difficult 

 to describe may be noticed on contrasting this with its related forms. 

 The luminous organs have a compact epithelium-like structure, 

 because the cells of which they consist are polyhedral and fit together 

 closely, whereas these cells are separated or even scattered in other 

 Pyrosomas. The stomach wall has a similar thin, epithelial texture. 

 In addition, the shape of the stomach is somewhat peculiar, being 

 cylindrical, long, and with squarish ends. The branchial sac pre- 

 sents a characteristic oval contour as seen in side view, its ventral 

 wall bulging strongly so as to give to the endostyle a strong even cur- 

 vature. This latter organ, it should be noted, is shorter than the 

 branchial region proper, a feature not found in other forms of the 



