12 PROCEEDIlSrGS OF THE ISTATIOlsrAL MUSEUM tol. 74 



X above. In addition to the pair of carinae connecting each basal and 

 the infra] acent IBB, a high, sharp keel passes from the center of each 

 basal to each adjacent plate. The radials vary considerably in size 

 and proportions. The arm facets vary in attitude from vertical to 

 being slightly inclined upward. The axial canal and food groove 

 are confluent, although in cases where the plates are well preserved 

 the axial canal is a narrow, deep channel sharply differentiated from 

 the broader V-shapecl groove above. In some cases it appears that 

 the canal is arched over and separated from the groove above. In 

 the anterior radial of one specimen the arm facet is greatly reduced 

 in size, and it may well be that in this case no food groove was 

 present. Below the groove and to either side is a triangular articu- 

 lating facet with the apex pointing to the center. Below and between 

 these facets is a well-defined triangular fossa, while above them is a 

 pair of shallower fossae. The surfaces of the articulating facets as 

 well as the margin of the arm facet are sharply crenulate. The 

 upper margin of the radial curves inward, forming a platform 

 around the margin of the tegmen. High, sharp keels pass from 

 radial to radial at the lower level of the arm facets. Two similar 

 keels likewise radiate from the arm facet to the inf raj acent basals. 

 Two brachials are preserved in one ray of each of two individuals. 

 In the small specimen the brachial is constricted in the median por- 

 tion, giving it a somewhat hour-glass shape. In the large specimen 

 the brachial is almost cylindrical. In neither case is the second 

 primibrach axillary. In the smaller specimen the arm covering plates 

 are beautifully shown. They consist of a double series of high inter- 

 locking plates, there being three pairs to an ossicle. 



There are three plates of the anal series incorporated in the cup. 

 RA is unusually large in some specimens, being as large or larger 

 than x. RA is pentagonal in outline and bears the customary rela- 

 tions to the adjacent plates. Plate x supports two tube plates. The 

 plates of the posterior interradius are traversed by series of plica- 

 tions similar to those on the remainder of the cup. 



The tegmen is partially preserved in three specimens. It is made 

 up of thin plates that apparently formed a weak structure. The 

 outstanding feature of the tegmen is the presence in each specimen of 

 a large knoblike madreporite. The openings of the canals penetrat- 

 ing the plate may clearly be seen in two of the specimens. In one 

 specimen what appears to be part of the ventral sac is preserved. 

 The sac is inclined upward slightly from the horizontal and curves 

 gradually to the left. It is compressed laterally and increases grad- 

 ually in size distad. Its point of inception is about on a level with 

 the arm bases and on the right side of the posterior interradius. 



