198 DISCOVERY REPORTS 



Side- and cover-plates are well developed along the arm and pinnule ambulacra. There 

 are two to three pairs of each to every pinnular (Fig. 20/). The side-plates have a wide 

 base produced into a column, to the ends of which the long and narrow cover-plates are 

 attached. In the older specimen the bases of the side-plates along the lower segments of 

 the pinnules are reduced. 



Sacculi are very few and inconspicuous, widely and irregularly spaced. 



The gonads lie as in A^. virilis in the angles between the pinnules and the arms. Only 

 two of the specimens are males ; both are rather small and probably far from physically 

 mature. Their testes are very much smaller and less conspicuous than those of A'^. virilis 

 though they are easily seen from the side. They are about 1-2 mm. long, triangular in 

 shape, lying with one side along the first two segments of the pinnule and another along 

 the arm. Regarding the side which runs along the arm as the base, there is near the 

 apex, but slightly below it on the inside, a small papilla through which I assume there 

 is a pore for the passage of the spermatozoa to the outside. 



The female reproductive organs consist of ovaries and brood-pouches as in A^. virilis 

 (Fig. 20 g). In the younger specimens the brood-pouch does not touch the ovary of the 

 next pinnule on the same side of the arm; in the older specimen from St. 1948 (which 

 is a female) it does. The ovaries are oval, less than i mm. long in the younger specimens, 

 about 1-5 mm. in the older. Each lies at the base of the pinnule, resting against it and 

 the arm, and is not usually visible behind the base of the pinnule from the outside. The 

 brood-pouch Hes in the angle between the arm and the pinnule, separated from the 

 ovary by a thin septum in which there is a large round pore. Larvae escape from the 

 brood-pouch by a slit-like orifice on the inside. The brood-pouches are easily seen from 

 the outside and their walls are so thin that the embryos, and the ciliated bands of the 

 most developed, may be seen through them. There are many more though much smaller 

 embryos than in A^. virilis. In the larger brood-pouches of the younger specimens there 

 may be over 30 embryos; one of the lower brood-pouches of the older specimen was 

 dissected out and found to contain no less than 92 embryos. The embryos vary in size 

 from 0-25 to 0-48 mm. The smallest are globular and only a little larger than the biggest 

 eggs in the ovary; the largest are oval with five broad bands of ciHa: they are fully 

 formed larvae at much the same stage of development as those of A'^. virilis described 

 by Mortensen (1920) which are four times as long and have no trace of ciliated bands. 

 They presumably pass on to a free-swimming stage before settling down and changing 

 into pentacrinoid larvae. The older embryos are found in the distal part of the brood- 

 pouch, the younger in the proximal part near the ovary. 



One brood-pouch may contain every stage between the egg and the fully formed 

 larva. I have not worked out the development. The fully-formed larva has two circles 

 of plates, the orals and basals, and at least two infrabasal plates. There are six to eight 

 stem joints ; I see no supplementary terminal plates. 



The younger specimens are of a pale straw colour in spirit ; the older has a dusky hue. 

 Some Mvzostomiim were found on the genital pinnules. 



