DESCRIPTION OF SPECIES i 3S 



Tentacles. There are twenty-two tentacles in one specimen examined. They have short branches 

 and are at most bi-pinnate. 



Dorsal tubercle. The dorsal tubercle in each of four animals has a narrow longitudinal slit-like 

 opening, either straight, slightly sinuous, or very slightly curved (Text-fig. 58 B). This is quite distinct 

 from the C-shaped opening described by Arnback in the typical form of the species. 



Branchial sac. The number of branchial folds varies ; in one animal there are seven on each side 

 and in another seven on the left and six on the right. There are six to fourteen longitudinal bars on the 

 folds and either one bar or none, between folds. 



Gut. In general shape the gut conforms to Arnback's description and figure, but the upwards 

 bend of the rectum is less acute, in the ' Discovery ' specimens. 



1.0 an 



Text-fig. 58. Molgula setigera Arnback f. georgiana (St. 474): A, specimen with test removed; B, dorsal tubercle; C, gonad 

 with one sperm duct; D, part of gonad with three sperm ducts. Molgula setigera f. marioni (St. 1563) : E, specimen with test 

 removed; F, dorsal tubercle; G, gonad. 



Gonads. The form of the gonads (Text-fig. 58 C, D) is fairly constant, resembling that of the type 

 specimens, but the gonoducts are variable. Usually the oviduct (od.) is moderately long, but in at 

 least one specimen is quite short ; it is always directed up towards the atrial siphon. The sperm ducts 

 (s.d.) vary in number and position. There may be from one to five short narrow sperm ducts near the 

 base of the oviduct. 



Remarks. These specimens from South Georgia have certain slight but constant differences from 

 Arnback's types of M. setigera, and I have hesitated whether to include them in that species or to 

 regard them as a new species. The presence of bristles only on the siphons, and the existence of 

 several sperm ducts are perhaps minor differences, but the condition of the dorsal tubercle is a more 

 important character. There is little doubt that the ' Discovery ' material from South Georgia is taken 

 from a genetically different population than that from the Falkland Islands on which the species was 

 founded. However, the remarkable similarities which all the specimens have suggest a very close 

 relationship which is perhaps best denoted by calling the South Georgia population a new form, 

 f. georgiana. Should more specimens become available from either Falkland Islands or South 

 Georgia, or from places between, it may be possible to revise the systematic position. 



