46o NORTH AMERICAN INDEX FOSSILS. 



3. Ambulacra spiral, at broad end of an elongated, pear-shaped calyx. 



III. Gomphocystites. 



3. Ambulacra not spiral c. 



c. Pores absent 33. 



33. Calyx flattened V. Amygdalocystites. 



33. Calyx subglobose XIV. Malocystites. 



c. Pores present 44. 



44. Pores piercing plates, without definite arrangement..!!. Holocystites. 



44. Pores piercing plates, with definite arrangement aa. 



aa. Pore-rhombs very numerous !V. Paleocystites. 



aa. Pectinate rhombs IO-15 V!. Glyptocystites. 



aa. Pectinate rhombs 3 f. 



f. Ambulacra two X!. Pseudocrinites. 



■j". Ambulacra three to five * 



* . Ambulacra undivided \'^ . 



\" . Ambulacra about half the length of the calyx ; distal 



portion of column fused IX . Lepocrinites. 



\'^ . Ambulacra usually extending to column. 



X. Jcekelocystis. 



*. Ambulacra branching 2'^ . 



2^^. Calyx plates 25 ; ambulacra branching slightly, rarely 



simple XII. Callocystites. 



2^^ . Calyx plates 18 ; ambulacra branching extensively. 



XIII. Sphcsrocystites. 



I. EocYSTiTES Billings. 



Calyx plates numerous, varying in size, form and ornamenta- 

 tion. Cambric. 



1. E.(?) longidactylus Walcott. (Fig. 1765,0.) Cambric. 

 Calyx plates without apparent order, and varying in form, size 



and surface characters on the same specimens. Plates smooth to 

 somewhat radiately sculptured, their margins indented, probably 

 indicating pores. Arms several, long, slender, biserial, with one or 

 two (?) pinnule-like plates arranged upon the one side of each 

 arm plates ; stem of numerous irregular small plates. 



Lower(?) Cambric (Pioche formation) of Nevada and Utah. 



2. E. primaevus Billings. (Fig. 1765,^.) Cambric. 

 Known only from calyx plates; these are polygonal, with strong 



ridges radiating from the elevated center. (Type of genus.) 

 Middle Cambric of New Brunswick. 



II. Holocystites Hall. 



Calyx elongated to subcylindrical, short stemmed or stemless, 

 composed of large plates in quite regularly alternating series, 



