A TAXONOMIC STUDY ON PYROSOMA — METCALF AND HOPKINS. 227 



position of the testis on the posterior rather than the ventral body- 

 wall, and especially the arrangement of the zooids in regular trans- 

 verse whorls. 



P. verticillatum is found in the Indian Ocean, where it was collected 

 first southwest of Ceylon, and again shortly afterwards west of the 

 Chagos Archipelago. It is reported also from the Pacific Ocean, 

 although it is probable that the Pacific specimens, if restudied, might 

 have to be referred to the variety (cylindricum) , which is found in 

 these waters. The species is by no means abundant, to judge from 

 the paucity of specimens obtained, hence it is not so well known as 

 others. 



PYROSOMA VERTICILLATUM CYLINDRICUM, new subspecies. 



Plate 22, figs. 14 and 15; plate 33, fig. 43. 



The form here considered is represented, as before mentioned, by 

 21 specimens taken during the Albatross Philippines Expedition 

 (1908-1909). x As these differ in several particulars from the species 

 just described, and since these distinctions are more or less constant, 

 it seems quite possible that we have here a geographical race or 

 subspecies confined to the Pacific Ocean. 



The cylindrical form of the colony is in contrast to the more ovate 

 form of P. verticillatum. As in P. verticillatum , a regular arrangement 

 of zooids obtains, even in the mature specimens. The largest colonies 

 attain a length of 3.4 cm., the majority, however, about 2.5 cm. The 

 width or thickness of the cylindrical trunk averages 1.2 cm. The test 

 is very much like that of P. verticillatum — firm, colorless, transparent, 

 and smooth except for the funnel-like depression over each oral 

 aperture (fig. 15). 



All the larger zooids — those which have taken up a definitive posi- 

 tion in the test — appear quite globular and short (fig. 15). In size 

 these range between 2.2 and 2.4 mm. in length, averaging 2.4 mm. in 

 height (dorso-ventrally) . These vary little in size or form or in the 

 character of their organs. There are always numerous small zooids 

 around the colonial aperture, those which have been formed most 

 recently as a result of budding. 



The atrium is very short and broad; the oral chamber — i. e., the 

 portion of the pharynx in front of the stigmata — is almost lacking. 

 On this account the zooids, examined in side view, appear circular 

 to quadrangular in outline. This appearance is emphasized by the 

 height of the branchial basket, which is higher than long. In the 

 better-known species, described below, the zooid is elongated, often 

 greatly so. 



i United States National Museum. Cat. Nos. 6468 (type), 6412, 6413, and 6414. The authors much 

 prefer the Latin form "tyi^us' in taxonomic reference, but they conform to the editorial usage of tho 

 United States National Museum. 



