A TAXONOMIC STUDY ON PYROSOMA — METCALF AND HOPKINS. 233 



Distribution. This species is at present known only from the 

 western Pacific Ocean, and was taken during the Albatross Philippine 

 Expedition, 1907-1910, at the following stations: 



D. 5319, China Sea, vicinity of Formosa; November 5, 1908: 20 

 fathoms; surface temperature 79° F.; one specimen (Type), Cat. No. 

 G416, U. S. N. M. Eastern Tropical Pacific Expedition. 



H. 3788 (A.A. 15), latitude 4° 35' N.; longitude 136° 54' W.; 

 600 miles north of the Marquesas Islands; September 8, 1899, 2,583 

 fathoms; surface temperature 80° F., one specimen, Cat. No. 6425, 

 U. S. N. M. 



PVROSOMA OPERCULATUM (Neumann, 1908). 



Plate 24, figs. 21-23. 



Only one specimen of this interesting form has been collected. 

 This was found in the Indian Ocean a little westward of the Chagos 

 Archipelago (Deutsche Tiefsee-Expedition, Station 228). The colony 

 is about 5£ cm. long and 3^ cm. broad. In form it is broad and cylind- 

 rical, roundly truncate at both ends, the closed end being somewhat 

 broader than the open end, the shape of the colony being thus unique 

 among the Pyrosomas. The surface of the test is quite smooth in 

 this species. 



The zooids are closely and irregularly placed in the test. They 

 attain a length of about 9 mm. The prebranchial chamber is of 

 moderate length; it is encircled by two circum-oral muscle fibers. 

 The branchial chamber in side view appears as a slightly prism- 

 shaped box, narrowed behind, with straight sides, as the endostyle 

 is not curved except at its extreme anterior end. There are about 

 40-45 rows of stigmata and 18-20 longitudinal branchial bars. 

 Dorsal languets, about 16. 



Gonads. The testis is composed of 15-17 tentacle-like lobes, and 

 in their midst, a sperm duct with a dilated, spherical receptacle. It 

 lies in an evagination of the body wall. This species is strongly 

 protogynous. Growing zooids, in which the embryo has reached the 

 tetrazooid stage of development, contain as yet only the rudiment of 

 a testis. 



The cloacal chamber is elongated and narrow, appearing three- 

 cornered in cross-section. In young zooids it may equal the length 

 of the rest of the body, but in older ones it is relatively shorter — 

 about one-half as long as the rest of the body. On the ventral border 

 of the cloacal aperture there is a prominent, hood-like valve (figs. 22 

 and 23), which is found in no other species of Pyrosoma. The edges 

 of the aperture are bordered by a narrow muscle band, probably 

 identical with the cloacal sphincter in other forms. The function of 

 this peculiar apparatus seems to be, as Neumann thinks, to prevent 

 the water in the colonial chamber from flowing back into the pharynx 



