232 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



debris in the zooids or any part of the colony to cause color. The 

 viscera of the zooids appear as dark-brown, opaque bodies, especially 

 the testes, which are of large size in this species. 



The form of the zooids as seen in side view is best described as 

 oval, some individuals being quadrangular or some elongated. In 

 size they vary from 2 to 2.6 mm. in height and from 3.2 to 4 mm. in 

 length, the average conditions being 2.4 mm. high and 3.7 mm. long. 

 It should be emphasized in this connection that throughout the colony 

 there is very great uniformity as to the size of the zooids. This is 

 strongly in contrast to conditions found in the three preceding forms 

 (P. verticillatum and its variety cylindricum and P. hybridum) . The 

 atrium in this form is of moderate length, i. e., from one-third to one- 

 half that of the branchial basket. The oral or prebranchial chamber 

 is rather short but never entirely lacking (fig. 18). 



The mantle is fairly firm in texture. Associated with it are the 

 muscles usual in the subgenus. These are the customary pair of 

 cloacal muscles — rather long and narrow — , oral and atrial sphinc- 

 ters, and two circum-oral ring fibers. 



The short prebranchial zone never exceeds one-fourth of the length 

 of the branchial basket. The mouth is small and shows the charac- 

 teristic " fringe" and ventral tentacle. The branchial basket is 

 nearly oval in side view, with slightly truncated posterior end. On 

 each side there are 16 longitudinal bars, occasionally only 15, and 27 

 to 28 stigmata! rows. The endostyle is peculiar in being shorter 

 than the branchial basket. Dorsal languets, 6 to 7. The luminous 

 organs are mostly oval. Each of the dorsal leucocyte masses is 

 small and distinct. A description of the digestive tract would corre- 

 spond very closely to that given for P. verticillatum cylindricum 

 The stomach may be relatively larger, but is still rather narrow and 

 rather square at the ends; the intestine is thicker and less sharply 

 bent upon itself. 



Gonads. In this species the zooids are protogynous. The egg ripens 

 early, and when considerably advanced in development, detaches 

 itself from the cloacal wall and moves up into the right peribranchial 

 space. The testis attains to a large size, and when mature is compact 

 and globular, protruding strongly beyond the ventral body contour. 

 It consists of about 18 finger-like lobes which are directed for the 

 most part upward and slightly forward. 



We see in this species, for the first time in this subgenus, an ap- 

 preciable narrowing and likewise a lengthening of the cloaca. The 

 reduced size of the atriopore is also characteristic, for although not 

 so small as in some (P. atlanticum and its several subspecies) it is 

 much more constricted than in the previously described members of 

 this subgenus. 



