172 ECHINODERMATA— PELMATOZOA phylum iv 



Cryptoblastus E. and C. Calyx sub-globose, with a flattened or slightly 

 hollowed base. Basals and deltoids small. Lancet-plate separated from the 

 radials by a hydrospire-plate, which does not extend above the radio-deltoid 

 suture ; but above this line the lancet-plate meets the deltoids without leaving 

 any hydrospire-pores. Spiracles round, distinctly double at four of the sides, 

 but those of the posterior side confluent with each other and with the anus. 

 Summit covered by numerous, irregularly arranged small pieces. Lower 

 Carboniferous (Burlington Group) ; North America. 



HeteroUasfus E. and C. Resembling the preceding in form and proportion 

 of its component parts. The proximal ends of the deltoids produced in short 

 spine-like processes, at the base of which minute lateral openings, one to each 

 deltoid, are visible. These openings lead into gutter-like channels excavated 

 in the substance of the plates for the reception of the proximal ends of the 

 two hydrospire- canals. Radial sinuses wide, their edges sloping gently 

 downwards to the slightly petaloid ambulacra. Lower Carboniferous ; 

 England and (?) North America. 



Mesoblastus E. and C. Calyx ovoid to globose, with concave to protuberant 

 base. Radials long, deltoids small, short, unequally rhombic. Ambulacra 

 very narrow, extending to the base. Spiracles, as a rule, distinctly double, 

 but sometimes incompletely divided. Lancet-plate entirely, or for the most 

 part, concealed by side-plates. Lower Carboniferous ; Belgium, England, 

 (?) North America and Australia. 



Acentrotremites E. and C. Calyx elliptical, with broad pentagonal lower 

 face. Radials large, taking up three-fourths of the height of the calyx. 

 Deltoids unequally rhombic, each notched by two spiracles at the ends of the 

 radio-deltoid suture. Anal opening situated close to the summit in the 

 posterior deltoid. Ambulacral edges of the deltoids without hydrospire-pores. 

 Lower Carboniferous ; England. 



Carpenteroblastus and Lophohlastus Rowley. Lower Carboniferous (Kinder- 

 hook and Burlington Groups) ; North America. 



(?) Ny7iiphaeoblastus von Peetz. Lower Carboniferous ; Russia. 



Family 7. Pentephyllidae Bather. 



Calyx stemless and suh-pentagonal ; radials, asymmetrical. Ambulacra linear, 

 extending down to the base ; one shorter than the rest. Carboniferous. 



Pentephyllum Haughton. Carboniferous ; Ireland. 



Family 8. Zygocrinidae Bather. 



Stemless. Calyx depressed, asymmetrical, quadrilobate. Four ambulacra 

 between the lobes, accompanied by a single hydrospire on either side ; fifth ambulacrum 

 shortened and widened. 



Zygocrinus Bronn {Astrocrinus Austin, non Conrad nee Miinster). Lower 

 Carboniferous • Great Britain. 



[The text lor tlie group Blastoidea in the present work has been revised by Mr. Frank 

 Sjjringer, of Las Vegas, New Mexico, and Washington, D.C. — Editor.] 



