A TAXONOMIC STUDY ON PYROSOMA — METCALF AND HOPKINS. 231 

 PYROSOMA ELLIPTICUM, new species. 



Plate 23, figs. 18-20; plate 33, fig. 44. 



A single, small colony of Pyrosoma, which differs in certain funda- 

 mental points from all other known forms, was taken by the Albatross 

 from the China Sea on November 5, 1908. In general appearance, 

 however, it does not seem to represent a sharply demarcated species. 

 One of the characters which distinguish it is the nearly complete 

 flattening of the colony as a whole, so that in side view it is oblong 

 with rounded corners and in edge view more nearly linear. (See the 

 end view, fig. 20, pi. 23.) 



Other characteristics are the regular, but not strictly verticillate, 

 arrangement of the zooids in the test; and certain differences in the 

 organization of the zooids. All these characters of the zooids are 

 rather uniform and constant, and all the zooids show about the same 

 size. The measurements of the specimen studied 1 are as follows: 

 Length, 4.5 cm.; width, 2 cm.; and mean thickness about 0.7 cm. 

 The open end is somewhat broader than the closed, as we might 

 expect. In correlation with the flattened condition of the colony, 

 the opening into its axial chamber is slit-like (fig. 20). At both 

 ends of the colonial aperature there is a broad expansion of the 

 diaphragm which effectually preserves the shape of the aperture. Any 

 attempt to pull the test into cylindrical form must result in a tearing 

 of this diaphragm at the ends of the ellipse. Hence, it is not probable 

 that the flattened form of the colony in our preserved specimens of 

 this species is due to any collapsing from mechanical causes. 



A close and rather uniform arrangement of the zooids obtains. 

 They lie in rows transverse to the long axis of the colony, but the 

 whorls thus formed appear more obscure than in any of the ver- 

 ticillate forms yet described. The zooids in one whorl lie generally 

 opposite interspaces between the zooids of the adjacent whorls, thus 

 forming somewhat obscure longitudinal rows. The arrangement, 

 however, is not perfectly regular. The oral apertures of the zooids 

 open flush with the outer surface of the test; hence there are no 

 funnel-like depressions in its surface such as are found in P. ver- 

 ticillatum. The zooids also appear more collapsed or flattened later- 

 ally. There are no processes or denticles on the test. In color the 

 colony in alcohol is yellowish-brown, the test itself being very clear 

 and transparent. The color is probably due in part to the test 

 absorbing color from the pigment cells on the esophagus of each 

 zooid. In our preserved specimens all the tissues of the zooids 

 appear brownish and the test is yellowish. There is no sediment or 



« Other specimens, doubtfully of this species, were taken in September, 1899, at a station 600 mile* north- 

 ward of the Marquesas Islands. (Station 3788— .4 Ibatross.) 



