11 a PROCEEDINGS OP THE ACADEMY OF [1886. 



Our Poteriocrinidie contain essentially the same genera as those 

 of Zittel, but we except from his list Homocrinus, Dendrocrinus, 

 Agassizocinnus and Belemnocrinus. For the two latter we pro- 

 pose distinct families. 



The Encrinidae are closel}^ allied to the Poterocrinidae, and we 

 think will ultimately be consolidated with them. Nothing, as yet, 

 is known of their ventral structure, but neither of that of the 

 Poterocrinidfe except their ventral tube. There is nothing which 

 proves that the ventral surface of Uncrimis was composed of soft 

 parts, or that it was exclusively perisomic or diffei-ed from that 

 of the Poteriocrinidse which are universally regarded as Palaeo- 

 crinoids. The only difference which we have discovered is that 

 in the Encrinidaj the brachials are united by syzygy and also 

 the proximal arm plates ; contrary to the Poteriocrinidffi in which 

 syzygies, so far as known, do not occur. 



Among Astylocrinidae^ which represent the free floating Palaeo- 

 crinoidea, we include Agassizocrinus and Edriocrinus, the former 

 with underbasals, the latter with basals only. It is very possible 

 that Edriocrinus will prove to be the type of a distinct family. 



The Catillocrinidae contain : Catillocrinus and Mycocrinus. 

 The allied Calceocrinidse only the genus Calceocrinus. 



These ten families are defined by us as follows : 



A. Hybocrinid^. Base monocyclic ; calyx large compared 

 with the arms. Basals 5, unusually large. Kadials irregular, the 

 posterolateral one either unrepresented or very much smaller, and 

 sometimes non-arm-bearing. Arms frequently undeveloped in 

 one or more rays, or recurrent and appressed onto the outer 

 surface of the calyx; simple, and without pinnules. Azygous 

 side composed of a single, large azygous plate, and frequently an 

 anal piece, which in form resembles the right posterior radial. 

 Ventral sac very small, consisting of a mere tumor-like protu- 

 berance. 



B. Heterocrinid.e. Base monocyclic. Calyx small ; plates 

 irregular. Basals 5, variable. Radials irregular, frequently com- 

 pound in one or more rays ; the right posterior radial smaller, 

 resting upon the azygous plate. Brachials consisting of two or 

 more pieces, united by syzygy. Of the succeeding arm joints 

 only every second, third or fourth one pinnule-bearing. Azygous 

 plate large; anal plate consolidated with the right posterior 



I 



