30 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



,,n 3251, ii 'ill coasl of L'nimak Island, June 14, 1S90, bottom temperature 

 37 5 F. : three sp< 



Station 3255, north coasl of Unimak Island, June 14, 1890, bottom temperature 

 37° 1'. : two specimens. 



The crucial temperatures for the development of the embryo are therefore in the 

 neighborhood of 37° and 3 F. 



In size the specimens range from R 39 mm. to R 60 mm. 



A brood pouch is formed by the strongly arched disk so that the basal portion of 



all five rays is brought together and the adjac marginal spines interdigitate. The 



cavity thus formed is crammed with tiny sea stars which are attached to a common 

 central mass by a long slender strand of tissue proceeding from the actinal interradial 

 area just external to the mouth plates. This thread of tissue may be as long as the 

 diameter of the sea star (2.5 mm.) or considerably longer. It enters the central 

 mass which appeal's to consist largely of the twisted and tangled ends of these elongate 

 larval organs. The surface of the mass shows numerous soft lobes, some of which 

 appear to be the ends of larval organs, as one may tease the mass apart. It then 

 shows a fibrous structure. There seemed to be about six or seven of these centers of 

 attachment in the mas of tiny sea stars removed from a specimen from station 3251. 

 In other words the mass was divisible into seven smaller clusters. The young were 

 closely crowded into the temporary brood cavity, and were pressed closely against 

 the actionstome. I PI. 10, fig. 4.) 



Anatomical notes, forma beringensis. — Skeleton: There are three quite regular 

 series of plates on the \ eut ro-lateral region of the ray, the superomarginals, infero- 

 marginals, and actinals, graduated in size from larger to smaller in the order named. 

 The superomarginals are prominently four lobed, the descending lobe overlapping the 

 ascending lobe of the inferomarginals, which tend to suppress their ventral lobe as 

 they are crowded by the similar actinal plates. There are fair-sized regular inter- 



inal papular areas, but the actinal series of papular areas may be suppressed in 

 sl.nder-iayed specimens; or in thick-rayed examples two incomplete series are present, 

 tlie inner between the actinal and the adambulacral plates. 



The carina] plates (pi. <>, tigs. 1, 2. 3) with three to five short irregular lobes, are 



r than all but a few dorsolateral plates and are crowded into an irregular zigzag 

 The plates strongly overlap one .•mother in the radial direction, without any 

 intermediate ossicles, and laterally overlap the dorsolateral plates which in shape are 

 irregularaly elongate or incipiently lobed and form a very irregularly meshed skeleton, 

 as in L. polaris Jcatherinae, I., p. acervata, and other species. A variable number of 

 dorsolateral plates with three or four lobes, similar in form to the carinals are larger 

 than the others, and are, like them, the most external of the skeleton. A maximum of 

 three veiy irregular series can be traced on either side at the base of ray. The mesh 

 i- completed by smaller plates without lobes, or with less obvious ones. Different 

 specimens vary in respeel to the robustness of the dorsal skeleton. (PI. 9, figs. 2, 3.) 

 II the plates average slightly thicker, the aggregate result is smaller papular areas. 

 The ambulacra] ossicles are fairly large and typical Of the genus, the two scries of 



pori - o„ either side being fairly close, since the channel is relatively narrow. Cor- 

 londing to the first 10 inferomarginals there are 28 or 29 adambulacral plates. 



