434 PELMATOZOA. 



or more interradials in the anal interradius. In Nanocrinus^ how- 

 ever, there are only four arm -bearing radials, one of which is 

 axillary. In the type -genus Gasterocoma, one of the basals is 

 notched for the anal opening, which is situated between it and the 

 first anal plate. The arms are recumbent or widely divergent, and 

 the stem is generally four-sided, and is perforated by four canals, 

 surrounding, or confluent with, a larger central canal. The two 

 principal genera of this family are Gasterocoi?ia (Epactocrinus) and 

 Nanocrinus, both of which are found in the Devonian deposits of 

 Europe. 



Family 12. Hybocrinidce. — The members of this small family 

 exhibit embryonic characters, and have a " monocyclic " base, 

 with imperfectly developed radials, and a very small ventral sac. 

 The basals are five in number, and are very large. The arms are 

 simple and without pinnules ; and one or more of them may be 

 undeveloped, or only represented by recurrent ambulacra which 

 run over the outer surface of the calyx. The genera included 

 by Wachsmuth and Springer in this family are Hybocrinus, Hybo- 

 cystites, Hoplocrinus, and Baerocrinus, all of which are confined to 

 the Ordovician rocks. 



Family 13. Heterocrinidce. — In this family are comprised Palseo- 

 crinoids with a relatively large ventral and small dorsal development 

 of the calyx. The basis, as in the preceding family, is " monocyclic," 

 thus differing from that of the Cyathocrinidce and Poteriocrinida, in 

 which underbasals are present. The arms are much more developed 

 than in the Hybocrinidcz, and are furnished with long pinnules. The 

 principal genera are Heterocrinus and Slenocrinus, both of which are 

 found in the Ordovician rocks of North America. 



Family 14. Anomalocrinidce. — In this family the only genus is 

 Anomalocrinus, the species of which are found in the Ordovician 

 rocks of North America. The calyx in this genus is large and 

 depressed, with a "monocyclic" basis. The pinnules of the arms 

 are not given off alternately from opposite sides (as in Crinoids 

 generally), " but from every successive joint on one side at a time, 

 from one bifurcation to the next, where they change on both rami 

 to the opposite " (Wachsmuth and Springer). 



Family 15. Belemnocrinidcz. — The only genus included in this 

 family is the Belemnocrinus of the Carboniferous Limestone of North 

 America. In this genus, the basis is "monocyclic," with no under- 

 basals, but with relatively large basals. The ventral side of the 

 calyx is well developed, but the visceral cavity is extremely small. 

 There is an anal plate placed in a line with the radials. The anal 

 proboscis is large and porous. Lastly, the pinnules of the arms are 

 given off regularly at every second or third joint, and not alternately 

 from all the brachials. According to Wachsmuth and Springer, the 



