242 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



compressed in this form, perhaps owing to the crowding of the 

 zooids in the test. 



The musculature of the zooids is well developed, and shows little 

 diversity of pattern. In addition to the oral sphincter there are two 

 distinct circum-oral fibers or rings varying in position according as 

 the oral chamber is long or short. When this is greatly elongated 

 they lie near its distal end, somewhat widely separated from each 

 other. The lateral muscles of the cloaca are quite prominent. 

 They are usually short. They lie about at the level of the digestive 

 tract; or they may be considerably posterior to the gut when the 

 cloaca is long, as is often the case. The cloacal sphincter is a small 

 thick ring which maintains an almost complete closure of the cloacal 

 opening in preserved specimens. 



The mouth differs very little from that of P. verticillatum subspecies 

 cylindricum. If anything, it is a little more constricted; while the 

 tentacular folds are even more pronounced. These number about 

 18 usually, not counting the true tentacle on the ventral border. 



The pre-branchial chamber is narrower than the branchial sac; 

 it is always present as a distinct cavity or siphon. It varies greatly 

 in length, often equaling the length of the branchial sac, or even 

 exceeding it (4 mm. or less). 



The branchial chamber proper varies from oval or quadrangular to 

 triangulate, narrowing toward the posterior end. Many times it will 

 be found to be even harp-shaped owing to the strong curvature of 

 the endostyle at its anterior end. 



In each wall of the branchial basket there are 14 to 15, occasion- 

 ally 16, longitudinal bars; 30 to 36 stigmatal rows. Dorsal languets, 

 from 6 to 10 in mature zooids; in small colonies (1.5 cm.) the normal 

 number is 4 to 5. 



The dorsal masses of leucocytes form organs which are more 

 prominent than usual, but they are not so distinctly separated. 



The ganglion is small, or of moderate size. In number and 

 arrangement, the nerves are as is typical for this subgenus (fig. 13, 

 pi. 22). Two pairs extend forward from the ganglion, four out to the 

 sides, and two backward. The third and fourth pairs of nerves are 

 sometimes difficult to identify, because the third often tends to fuse 

 for a distance with the second, and the fourth nerve is never very 

 distinct at best. 



The luminous bodies are comparatively large: in form they are 

 oval or oblong, or sometimes circular as seen in side view. 



Digestive tract. In this, as in the subsequent varieties of this 

 species, the stomach is larger and more spherical in appearance than 

 we have found it to be in the species we have thus far described; 

 while the intestine is thick, and forms a round rather than a sharply 

 bent loop. There have been demonstrated, for these forms also, 



