238 DISCOVERY REPORTS 



So far as the essential structure of skeleton is concerned this species completely 

 bridges the gap between Attasterias and Lysasterias. 



The type of A. mimita is in the Museum d'Histoire Naturelle (E 792 Hombron et 

 Jacquinot, 1847, alcohol). Perrier considered the type locality to be Port Famine, 

 Magellan Strait, and hence probably from very shallow water. 



I have also studied 2 dried specimens from Darwin Habour, Choiseul Sound, Falkland 

 Islands (No. 2623 Museum of Comparative Zoology). The smaller measures R 18 mm., 

 r 6 mm. ; the larger R 48 mm., r 13 mm. In the smaller example the abactinal skeleton 

 is clearly visible and consists of a weak, irregular reticulum resembling the condition of 

 A. pedicellaris as figured by Koehler (1923, pi. 5, figs, i, 4) and closely similar to that of 

 the type specimen of minuta. Most of the superomarginals carry one spinelet and the 

 inferomarginals two, while scattered along the intermarginal channel and inside the 

 furrow margin are rather numerous, lanceolate, straight pedicellariae two-thirds the length 

 of the superomarginal spinelets. In the larger specimen, however, the abactinal integu- 

 ment is thickened and conceals the skeleton, which is quite weak and irregular as in 

 Koehler 's pi. 5, fig. i, alluded to above. The proportions are about as in fig. 4. There are 

 a few actinal plates and spines at the base of the ray and the adoral carina is composed of 

 3 pairs of contiguous adambulacrals, the first pair larger than second, and the second 

 larger than third. The superomarginal spines have been mostly absorbed ; pedicellariae 

 as in the small example. A third specimen (no. 2624) carries a cluster of young. 



In the United States National Museum are 25 specimens from Port Stanley collected 

 by Dr W. L. Schmitt (Fisher, 193 1, p. 7). 



None of the young of pedicellaris (accompanied by adults) which I have examined 

 exhibit such a degeneration of skeleton as is shown in Koehler's figures (1923, pi. 5, 

 fig. 5 ; pi. 6, figs. 3, 10). The specimens which I feel fairly certain are young stages of the 

 adults called pedicellaris have narrow rays, numerous abactinal spinelets, a small meshed, 

 complete abactinal skeleton, and a thinner skin lacking pustules. Lanceolate pedicel- 

 lariae small, few or lacking. 



But one specimen of mimita (R 31 mm.) from St. 55 has more numerous abactinal 

 spinelets and thinner skin than the others, and at the same time differs from an example 

 of pedicellaris (R 36 mm.) from the same station in having a weaker skeleton, much 

 fewer straight and crossed pedicellariae. 



The explanation of the confusion may be that mimita is the not fully grown stage of a 

 weak-skeleton forma oi pedicellaris such as Koehler's pi. 5, fig. i, from West Point 

 Island, West Falkland. This form would usually have few abactinal spinelets and few 

 crossed pedicellariae, but numerous straight pedicellariae. The other extreme would be 

 represented by the multispinous young and adults with a close-knit complete abactinal 

 skeleton and usually abundant crossed pedicellariae, but with very few straight ones 

 when R is less than 25 mm. 



So far as skeleton is concerned the varieties of such a polymorphic species would fall 

 in Sporasterias, Anasterias and Lysasteriasl 



