NO. 19S9. ASCIDIANS FROM NORTHEASTERN PACIFIC— BITTER. 451 



Table 8, made by arranging the specimens on the basis of the num- 

 ber of gonad lobes, brings out the fact that all the Atlantic specimens 

 (5) fall into a group with 12 or more gonads, while all the Pacific- 

 Bering Sea specimens (16), with one exception, fall into a group having 

 8 or fewer gonads. This result is in agreement with Huntsman's 

 conclusion that the Pacific animals have fewer gonads than have those 

 from the Atlantic-Arctic region, and favors the recognition of two 

 specific groups. Whether a single difference ought ever to be con- 

 sidered sufficient for separating species may be a question; but when, 

 as in this case, it is associated with one or more other highly probable 

 differences there should be no hesitation. As shown by Table 7, it is 

 almost certain that the spines of the test are arranged in circular 

 groups more definitely in the Pacific animals. The greater average 

 ratio of length to diameter shown by the Pacific specimens — 1.77:1 

 as against 1.20:1 for the Atlantic animals — is likely to prove a good 

 character also, but the distorted condition of many of the preserved 

 specimens makes measurement rather unsatisfactory. 



Since the specimens upon which Pallas based his Ascidia auran- 

 tium were from the Kurile Islands, that specific name will stand for 

 the Pacific animals, and the name of the Atlantic species will be H. 

 vyriformis (Rathke.) 



TABLE 8. 



Data of the Aurantium group of Halocynthia arranged with reference to the number of 

 gonads and bringing out the distinctness of H. jpyriforviis from U. aurantium. 



1 The numbers correspond to the numbers of the individuals in Table 7. 



The variation of the hypophysis should be mentioned, since it is 

 impossible to present this in the table. In small individuals the 

 hypophysis mouth is generally broadly horseshoe-shaped, the horns 

 being rolled in at the tips to the extent of one or two turns. With 

 increase of size this simple condition is lost, seemingly in all cases, 



