42 University of California Publications in Zoology. IT OL - 4 



the testes further back and disposed in a number of spherical 

 lobes. 



This species falls into the section of the genus in which the 



zooids are long, slender and uniform in outline, and with P. 

 obcsiim (Sluiter 1898), from the South African coast, represents 

 about the extreme in this direction. In the character of the atrial 

 languet and stomach folds, however, these two species are dis- 

 tinctly differentiated from each other. 



A single colony, Station 4420. (See data under Didemnum 

 opacum. 



Didemnum opacum, n. sp. 



PL 3, figs. 4(1 ami 41. 



General ('li</r<icl< rs <>f the Colony. Narrow elongate (in the 

 single specimen seen), thickness varying in different parts from 

 1 mm. to 3 or 4 or 5 mm. in places where well defined, rather 

 pointed pyramidal elevations are present. Prevailing color dull 

 brown with traces of green, but where the brown is absent the 

 test is made white by the closely crowded calcareous spicules. 

 Position of the zooids for the most part distinct by reason of 

 the absence of the spicules which are very abundant in all the 

 surrounding test. Zooids rather crowded, evenly distributed, no 

 common cloacal orifices on the colony at hand. Length 3.5 cm., 

 width in broadest part 1.3 cm. Attached by whole under surface 

 to a fragment of silicious sponge. X picnics very abundant, 

 especially concentrated in a thin layer slightly beneath the 

 surface of the test, but scattered through the whole test, of the 

 stellate form characteristic of the genus, but irregular in both 

 size and conformation, the rays varying from pointed to truncate, 

 and presenting always a more or less positive striate appearance. 

 A massing of spicules into three distinct groups about the bran- 

 chial orifice of the zooids, clearly visible to surface inspection of 

 the colony as three white bodies equally spaced around the orifice. 



Zooids. Small, much contracted, probably not more than 2 

 mm. long when fully extended, thorax and abdomen seemingly of 

 about equal length and not very sharply set off from each other; 

 Mantle muscle-bands few, running obliquely backward from the 

 anterior end. 



