520 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The IBrj and IBr., are about equal in length, very narrow, and of the usual 

 shape. The width of the base of the IBr, is about half that of the distal border 

 of the radial. 



The arms consist of about 17 brachials, each with an ambulacral lappet, a 

 group of tentacles, and a sacculus. Very long slender pinnules are developed on 

 the eleventh or twelfth and following brachials. 



The total length is about 13 mm. ; the crown (with the arms) measures 3 mm. 



So far as we are able to judge, this pentacrinoid is the young of Heterometra 

 quinduplicava, Stephanometra spicata, S. monacantha, or Lamprometra protectus. 

 As the last is by far the commonest of the four, it is probably to this species that 

 the pentacrinoid should be referred. 



TROPIOMETRA PICTA. 



During a visit to the island of Tobago, British West Indies, in March and 

 April, 1916, Dr. Th. Mortensen obtained a large series of the larvae of this species. 

 He writes me that he hopes to complete his report upon them in the near future. 



So hardy were these little pentacrinoicls that Doctor Mortensen was able to 

 bring a number of them living to New York. 



PTILOMETRA MULLERI. 

 Figs. 939, p. 549, and 122S, 1229, 1230, pi. 37. 



In February, 1898, the Australian steamer Thetis dredged off Manning River, 

 New South Wales, in 22 fathoms, a large number of pentacrinoids of this species 

 which were attached to the pinnules of young individuals. 



This is the only case yet recorded of the attachment of pentacrinoids to the 

 pinnules and not to the cirri of larger specimens. Attachment to partially grown 

 individuals in preference to adults is duplicated in the case of the pentacrinoids 

 of Comactinia nieridiondlis from Yucatan. 



Dr. H. L. Clark has described these pentacrinoids. He says : 



The youngest stage observed has a short, rather fleshy stalk, with a large attaching disk 

 at one end and the somewhat ellipsoidal body at the other. At this stage the joints of the 

 stalk appear as more or less discoidal plates, while the body wall contains 10 large plates 5 

 orals and 5 basals. No radial plates are visible. 



In a specimen a trifle older the radials have arisen in the space bounded by two oral and 

 two basal plates, and the stem joints are not so discoidal. 



At a still later stage the radials are conspicuous, though the orals and basals are equally 

 prominent, the first costal [IBn] and the costal axillary [IBr 2 ] appear as rather elongated 

 plates, and the arms consist of two or three joints; the stem, which is relatively far more 

 slender than at the earlier stage, consists of 10-12 joints, of which the middle ones are longer 

 than wide and are encircled at the mid-zone by a conspicuous ridge, a possible Indication of 

 a circle of cirri in some ancestral form. A similar ridge occurs on the stem joints of Meta- 

 crinus cingulatus (and other species of the genus), where it appears to be purely ornamental. 1 



1 The conspicuous ridge encircling the columnals at the mid-zone is, of course, the outer edge of the 

 primitive median annulus, and has no relation whatever to the ridges on the columnals of Metacrinus. 

 Cirri are formed on the outer ends of canals which, extending from the central organ outward, pierce the 

 secondary deposit of calcareous substance in the nodals or in the centrodorsal. It would be quite impos- 

 sible for them to occur on the periphery of the median annulus. 



