MONOGHAPH OF THE EXISTING CBINOIDS. 559 



There are about 20 brachials, which have prominently spinous distal borders. 

 Each brachial bears a pair of sacculi, but there are no covering plates. 



On at least two arms there is a rudimentarj' pinnule on the fourteenth brachial. 



The orals, which resemble those of Promachocrinus but are more delicate, more 

 nearly flat, and much more spinous distally, are separated from the distal border 

 of the radial circlet by a naked strip of perisome about equal in width to half the 

 length of the IBfj. 



FLOROMETRA SERRVTISSIMA. 



During a visit to Puget Sound Dr. Th. Mortensen was so fortunate as to secure 

 a considerable series of the pentacrinoids of this species, which he intends to 

 describe in the near future. 



HATHROMETRA PROLIXA. 



Figs. 1213, pi. 34; 940, p. 549, and 1227, pi. 3T; pi. 5C, fig. 1353; and part 1, fig. 409, p. 317, pi. 3, 

 fig. 532, 535, 53S, pi. 4, figs. 542, 544, and pi. 6, figs. 559-564. 



On the cirri of specimens of Hathrom^tra prolixa dredged by the Danmark 

 off northeastern Greenland, in 304 meters, on July 22, 1908, Dr. Th. Mortensen 

 found numerous pentaci'inoid larva representing several developmental stages. 



As a rule, these occurred on about the middle of the longer peripheral cirri, 

 sometimes two together; more rarely they were found on the shorter distal cirri. 



The youngest specimen was only 1.4 mm. long, the length of the column 

 being 1 mm. and that of the calyx 0.4 mm. It possessed about 10 columnals, of 

 which the central were the longest, 0.15 mm. in length by 0.05 mm. in breadth, 

 with the primitive median annulus very distinct and somewhat raised. The ter- 

 minal stem plate was circular. 



In another, which measured 2.5 mm. in total length, the column being 2 mm. 

 and the calyx 0.5 mm. long, there were 15 columnals, of which the three proximal 

 were quite short, but not broader than the succeeding. In the fourth coliimnal 

 the portion distal to the primitive annulus was somewhat elongated, the proximal 

 part remaining short. The following columnals were elongated, cylindrical, but 

 with the median annulus distinct, the longest measuring 0.25 mm. in length and 0.05 

 mm. in breadth. The terminal three or four were somewhat shorter. The terminal 

 stem plate was small and slightly lobed. 



The basals were slightly convex, trapezoidal with straight edges, the upper 

 border being finely undulated, corresponding to the lower border of the adjacent 

 oral. The proximal portion consisted of an irregular meshwork, while the distal 

 was quite regular in structure, the holes in the meshwork being arranged in straight 

 lines. Moi-tensen notes that this indicates that the proximal portion represents 

 the plate in its original size, the regular distal portion representing additional 

 growth, and as additional evidence for this view he notes that the regular distal 

 portion becomes more extensive with age. The same feature was observed in the 

 orals. 



The most searching investigation failed to disclose the presence of infrabasals. 

 I can confirm this statement, for at the time Doctor Mortensen was studying these 

 pentacrinoids I was in Copenhagen, and we both went over the material together. 



