144 



ECHINODERMATA PELMATOZOA 



SUB-KINGDOM III 



[The genus Carpocrinus was described by Miiller as having no anal plate ; 

 but according to Angelin the type-species (C. simplex) has an IRA interposed 

 between the radials. It must therefore be referred to Habro- 

 crinus, which it resembles in all other respects.] 



Desmidocrinus, Ang. (Fig. 247). Like the preceding, but 

 with a greater number of arms, which are longer, and composed 

 of shorter joints. Silurian ; Gottland. 



Periechocrinus, Austin (Geocrinus, d'Orb.) Calyx large, elon- 

 gate, somewhat urn-shaped, and composed of thin plates. R and 

 primary Br long and narrow, frequently bearing a median longi- 

 tudinal ridge. Distichals two ; interradials very numerous, the 

 second row composed of either two or three plates. Plates of 

 the tegmen very small. Anal opening sub-central, sometimes 

 prolonged in a tube composed of small, thin plates. Arms 

 numerous, slender, branching, biserial ; pinnules long and thin. 

 Column round, pierced by an extremely large axial canal. 

 Silurian ; Gottland, England, North America. 



Megistocrinus, Owen and Shum. Devonian to Middle Sub- 

 Carboniferous ; North America. Abacocrinus, Ang. Silurian ; 



Desmidocrinus 

 heterodactylus, Ang. 

 Silurian ; Gottlanc 



AnS). siz ' r Europe. Gennaeocrinus, W. 

 Group) ; North America. 



and Sp. Devonian (Hamilton 



Family 4. Barrandeocrinidae. Angelin. 



Base monocydic. Basals three, enclosing an anal plate which supports three inter- 

 Arms biserial, recumbent ; pinnules, exposed, and directed upwards. Silu- 

 rian ; Gottland. 



Barrandeocrinus, Ang. R followed by two costals ; the upper ones giving off 

 two heavy arms, which in perfect specimens are so closely folded as to conceal 

 the calyx completely. Pinnules very long; their tips bending inward from 

 opposite sides. Column cylindrical, and very heavy ; axial canal circular. 

 Silurian ; Gottland. 



[This genus is referred by Wachsmuth and Springer to the Batocrinidae 

 and the family discontinued.] 



Family 5. Reteocrinidae. Wachsmuth and Springer. 



Monocydic or diet/die. Infrabasals, when present, five ; basals four to Jive. Radials 

 separated by a large IRA which supports a vertical row of higher anals all of nearly 

 the same size the upper ones passing gradually into the tegmen. The spaces to either 

 side of this row, as well as the whole of the four other interrays, both in the dorsal cup 

 and tegmen, paved with minute, irregularly formed pieces. Ordovician. 



Reteocrinus, Bill. Calyx obconical ; interradial and interaxillary areas 

 profoundly depressed. IB five, differing considerably in size. B five, large, pro- 

 tuberant, hexagonal. R and fixed brachials forming a broad, highly elevated 

 ridge, which passes insensibly into the arms. IE in contact with the B, and 

 consisting of a large number of minute, irregular pieces. Tegmen composed of 

 numerous, very small, convex plates, irregularly arranged. Arms with strong 

 pinnules, and branching in the free state. Column sub-pentagonal. Ordovician ; 

 North America. 



