628 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



males are expanded, but to a lesser extent and consequently less asymmetrically than 

 in the females. 



In one brood pouch examined by Dr. John there is one egg, a larva similar to 

 that of vivipara figured by Mortensen as a full grown larva (1920, pi. 22, fig. 8) and 

 three other larvae with the plates better developed so that the orals and basals are 

 in contact. Similar larvae were found in the brood pouches of the female from the 

 Ross Sea, one of which contained seven larvae. 



Some of the syntypes have a sharp calcareous plate on the disk at the apex of 

 each interradius with its apex projecting over the peristome. The sides are curled 

 upwards. The bases of the plates are not distinct but appear to be straight. Dr. 

 Dilwyn John concluded that these plates are secondary perisomic orals. There are 

 no other plates on the disk. 



The sacculi are inconspicuous. They are often fairly regular on the pinnules, less 

 so on the arms; they also occur on the disk. 



The pinnule ambulacra are protected by large side and cover plates, of which 

 there are three pairs to each segment. The side plates overlap, forming a continu- 

 ous wall so that the individual ones are hard to distinguish. The cover plates are 

 more rounded with a fanlike system of supporting rods terminating in peripheral 

 spikes. They thus resemble the cover plates of I. challengeri, angustipinna, vivipara 

 and flavescens. The tentacles contain strongly knobbed spicules. 



The color in life varied from "pale dirty yellow-white" through "pale straw yel- 

 low" and "pale yellow brown" to "deep orange brown." The bases of the cirri may 

 be darker in color and the perisome have a faint greenish tinge. 



[NOTE BY A.M.C.] In 1939 Dr. Dilwyn John referred to I. graminea some 

 specimens taken by the B.A.N.Z.A.R.E. off Enderby and MacRobertson Lands on 

 the far side of the Antarctic continent from both the Graham Land peninsula and 

 the Ross Sea. These differ from the types most notably in having PI larger than 

 P 2 and with at least two more segments rather than one less. The relative propor- 

 tions of the first two pinnules seem to be subject to such small variation in the three 

 other species of Isometra where more than a few specimens are known (namely vivi- 

 para, flavescens and hordea) that I cannot agree with this inclusion. I am therefore 

 separating off these B.A.N.Z.A.R.E. specimens as a distinct species, Isometra johanni. 



Localities. Discovery Investigations station 190; Bismarck Strait, Palmer Archi- 

 pelago (lat. 6456' S., long. 6535' W.); 93-130 meters; at 100 meters, temperature 

 0.31 C., salinity 33. 89/ 00 ; ?stones, mud and rocks; March 24, 1927 [John, 1938] 

 (1 female, 1 broken specimen and fragments, B.M.). 



Same station, 100-130 meters (1 male, B.M.). 



Discovery Investigations station 1652; Ross Sea (lat. 7556' S., long. 17835' W.) ; 

 567 meters; at 540 meters, temperature 1.90 C., salinity 34.85% ; mud; January 

 23, 1936 [John, 1938] (3 males, 1 female, B.M.). 



Discovery Investigations station 1872; Bransfield Strait (lat. 6330' S., long. 

 5403' W.); 247 meters; at 200 meters, temperature 1.66 C., salinity 34.53 / 00 ; 

 soft mud; November 12, 1936 [John, 1938] (1 female, B.M.). 



Type locality.- All the specimens recorded above are syntypes. Since the three 

 stations are widely separated it is desirable that a restricted type locality should be 

 given and a lectotype selected. I therefore select the specimen from station 1872 in 

 the Bransfield Strait; this is the fifth one given in table 15 (p. 620). 



Geographical range. Known from the Palmer Archipelago, Bransfield Strait and 

 the Ross Sea. 



