. 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

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. 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.