ASTEROIDEA 255 



channel are a few simple lanceolate pedicellariae, which are found also in the inter- 

 marginal channel and abactinally. 



From Undine Harbour (including St. 25) and Leith Harbour (St. 1941) are 4 speci- 

 mens sufficiently different to constitute a well-marked variety, forma eimota, which is 

 characterized by conspicuously protruding abactinal spines, with narrower collars, an 

 exposed madreporite, a stronger abactinal skeleton, a much shorter series of hidden 

 actinal plates, and actinal papulae which are largely suppressed on rays (Undine 

 Harbour), or are small and form only a short series (St. 1941). There is a variable number 

 of straight pedicellariae, as in typical form (see PI. XXI, figs, i, 2). The type, Undine 

 Harbour, has 9 rays; R 100 mm., r 29 mm., br 20 mm.; madreporite circular, 4-5 mm. 

 in diameter, the inner border 16 mm. from centre of disk, hence rather more than half 

 of r from centre. 



The largest specimen of the typical form (St. MS 6) has 9 rays ; R 130 mm., r 36 mm., 

 br 22 mm. The disk is arched and rays approximated to form a brood chamber around 

 the mouth. In this were 707 young, ranging in diameter from 375 to 5 mm. ; date, 12 

 January 1924. Random sampling gives the following counts for the number of rays: 

 74 have 8 rays; 36 have 7 rays; 16 have 9 rays; 5 have 6 rays; 2 have 10 rays; i has 5 

 rays — surely an astonishing variation. An adult 6-rayed octoradiata will give the future 

 systematist something to puzzle over. Except for its mostly monacanthid adambulacrals 

 it could hardly be distinguished from Diplasterias meridionalis. 



A large 8-rayed specimen from St. 145 (7 January 1927) has the brood chamber filled 

 with young in the same stage of development as those from St. MS 6. These young have 

 been left undisturbed but a considerable number had already shaken loose. Sixty-seven 

 have 8 rays, 34 have 7 rays, 8 have 9 rays, 2 have 6 rays. There is a " Siamese twin " with 

 2 mouths and 13 rays. Two undeveloped eggs are 3-5 mm. in diameter. 



The young from St. MS 6 have 12-14 pairs of tube-feet. There is as yet no mouth, but 

 on the arched abactinal surface of the largest a few tiny papillae have appeared. Many 

 are greatly distorted by mutual pressure due to crowding, and in some cases i or 2 rays 

 are larger than the others. The young have long "umbilical" cords proceeding from an 

 interradius by which they are united in clusters to a common small, fleshy, lobed mass, 

 such as I figured for Leptasterias arctica (1930, pi. 10, fig. 4). The cord is o-o34-o-i7 mm. 

 in diameter and varies in length from two to five times diameter of young. Some- 

 times a cluster is anchored to a tube-foot by a loop of a cord which has cut into the 

 skin. 



A series of specimens from St. MS 10 includes the following graded sizes: R 6 mm. 

 (7 rays) ; R 7 mm. (8 rays) ; R 7-5 mm. (9 rays) ; R 10 mm. (7 rays) ; R 14 mm. (8 rays) ; 

 R 15 mm. (8 rays) ; R 21 mm. (8 rays) ; R 26 mm. (7 rays) ; R 30 mm. (8 rays, St. MS 6) ; 

 R 46 mm. (8 rays). In the smallest specimen the tube-feet are biserial but the second has 

 indications of a quadriserial arrangement. The fourth, with R 10 mm. and 7 rays, 

 would pass for a young D. meridionalis but a majority of the adambulacrals are mona- 

 canthid, with a scattering of diplacanthid plates. In this the occurrence of diplacanthid 

 plates is about as frequent as in the third specimen with 9 rays which could not be 



24-2 



