148 SYNOPTIC COLLECTION. 



We reach a condition in Glyptosphaera (PI. 255, G. 

 leuchtenbergi} in which the body plates are perforated, 

 the pores being in pairs. The ambulacra are on top of 

 the body plates, as in Mesocystis. They are long, nar- 

 row, and branching, and are apparently without pores. 

 They lead to the mouth which is covered by plates. 



The body of Echinosphaerites is globular, as shown by 

 PI. 257 (E. aurantium Rising); the specimen (No. 256) 

 is somewhat distorted by pressure, though with this 

 exception it shows the characteristic features well. The 

 body is protected by irregular plates (No. 256; PL 257) 

 and provided with two or three small imperfect arms 

 which are broken off in most specimens. Just under a 

 thin limy film covering the outer plates of the body there 

 are ducts (No. 256), the openings to which are arranged 

 in the form of rhombs, and they are therefore called 

 "pore-rhombs" (see No. 256 and PI. 257). These ducts 

 pass horizontally from one plate to the other, but the 

 pores of the rhombs communicate with short canals that 

 pass vertically through the plates. Probably these canals 

 and pores aided in respiration. The mouth in Echino- 

 sphaerites is at the apex, while the anus is on one side 

 (No. 256) protected by a pyramid of plates, as shown in 

 both specimen and figure. Between the mouth and 

 anus, a little to the right of the former, is the genital 

 pore (No. 256; PI. 257). 



One of the more specialized Cystoids is Caryocrinus 

 ornatus Say (Nos. 258, 259). The stem by which it was 

 fastened (not seen in the specimen) was composed of 

 many discs. Above the stem was the body, protected by 

 circles of regular plates, finely seen in No. 258. The 

 basal plates compose the first circle and above these is 

 the circle of radials (No. 259). In this genus the plates 

 at the base of the arms, often called interradials, perform 

 the work of true body plates. The arms were perhaps 

 little appendages like pinnules, but are usually broken 

 off, as in the specimens. The ambulacra in the middle 



