AMASTIGIA 325 



The relationship of A. gaussi to A. nuda and A. harmeri seems to be comparable to 

 the relationship of the Antarctic type of Caberea darwinii to the minima type and 

 C. glabra (see p. 383). It may seem inconsistent to have given them different taxonomic 

 status. My reason is that in C. darwinii such characters as the number of spines and 

 the size and length of zooecia intergrade so that no satisfactory line of demarcation 

 is to be found. In Amastigia gaussi these relative differences are coupled with a 

 positive character in the presence or absence of the giant spines with constricted base, 

 and it can thus be distinguished with precision from A. nuda. 



4. Amastigia benemunita (Busk). Figs. 2 A-C, 3 A, B. 

 Menipea benemunita Busk, 1884, p. 19, pi. iv, figs. 4, \a. 

 Amastigia benemunita Harmer, 1923, pp. 331, 333, 334 (references). 



Station distribution. Sub- Antarctic: South Atlantic Ocean, Sts. 388, 399, 1902, WS 76, 

 WS79, WS80, WS82, WS84, WS85, WS87, WS88, WSi28, WS231, WS237, WS243, 

 WS 244, WS 245, WS 246, WS 755, WS 765, WS 776, WS 781, WS 836, WS 838, WS 871. 



Geographical distribution. Gough Island (Discovery) ; Magellanic Region (Jullien ; Discovery) ; 

 Patagonian Shelf (Busk; Hamburg Museum, B. 809, B. 812; U.S. National Museum; Discovery); 

 off Patagonian Shelf down to 339 m. (Discovery; Chile (Busk)). 



Harmer noted that two apparently distinct types of basal heterozooecia may be found 

 in Amastigia benemunita, resembling those of A. rudis and A. nuda respectively. The 

 Discovery material has both kinds, but the variation in form and resemblance to 

 avicularia of other species only concern the shape of the avicularian chamber, while 

 the mandible and the beak, or groove, in which it lies are relatively constant, except in 

 size, and differ in shape from those of both A. rudis and A. nuda. 



The avicularian chamber may be more or less L-shaped, with a smaller transverse 

 limb, ending in the rootlet-chamber, and a larger longitudinal limb (Figs. 2 A, 3 A) as in 

 A. rudis; or it may be almost oval (Fig. 2 B) as in A. nuda; and intermediate states, 

 such as that figured by Levinsen, are found. The proximal limb when present varies in 

 shape and, in narrow branches, where heterozooecia of opposite sides meet, may be 

 considerably distorted (Fig. 3 A). The mandible is apt to be small, or even absent, in 

 these irregularly shaped avicularia. In A. rudis (Harmer, 1923, p. 332) the seta is long 

 and slender, and its articulating base has the asymmetrical structure of the true 

 vibraculum as understood by Waters (1913^. 481). The groove in which it lies is some- 

 what twisted and its outer border forms a lobe over the articulation. The mandible of 

 A. nuda (Fig. 2 D and Harmer, 1923, pi. xvii, fig. 25) is relatively broad with convex 

 sides, and the calcareous parts into which it fits are completely symmetrical and lie in 

 a plane parallel to the surface of the branch. In A. benemunita the mandible is setiform 

 with concave lateral borders (Fig. 2 A, B) and lies in a plane slightly oblique to the 

 surface of the branch; but the seta, which is shorter than that of A. rudis, is a true 

 mandible with a symmetrical base. The groove is slightly asymmetrical, but there is no 

 lobe. Harmer stated that the single basal heterozooecium in the Challenger specimen 

 (87. 12.9.70) of A. benemunita resembled those of A. nuda, but re-examination in the 



