302 PROCEEDINGS OF THE ACADEMY OF [1885. 



ponding number of water pores. The mouth is central, except 

 in a few genera, and the anus subcentral or excentric. The 

 genital glands are lodged in the lower parts of the arms, but are 

 usually fertile only in the pinnules. 



The Subdivisions of the Palseocrinoidea. 



Among the Palaeocrinoidea we recognize three great divisions, 

 which on the whole correspond to our former groups, Sphoeroido- 

 crinidae, Echthyocrinidse and Cyathocrinidae. These groups, 

 which arc divisible into definite subgroups, will be ranked by us 

 as suborders of the Palseocrinoidea, and the subgroups as fami- 

 lies. The three suborders, for which we have proposed the names 

 Camarata, Articulata and Inadunata, are distinguished from one 

 another principally by the mode of union among the calyx plates, 

 and the condition of the arms as to whether their lower plates 

 constitute a part of the calyx, and as such enclose the visceral 

 cavity, or form parts of the free arms. These groups are not 

 only well defined in nature, as shown by the fact that they are so 

 readily recognized, but they are also most convenient for all de- 

 scriptive and comparative work. 



When we first defined the three groups (Rev., i and ii), we laid 

 the greatest stress upon the construction of the ventral surface, 

 which, as we stated, offered most excellent characters for their 

 separation ; but as the modifications which take place among 

 them, to a large extent, result from the conditions of calj-x and 

 arms, we regard the structure of their ventral side as of subordi- 

 nate rank. This necessitates a re-description of those groups, 

 especially as our present views upon the ventral plates generally 

 differ essentially from those previously held by us. 



We have stated that the so-called "orals," upon which the 

 "Cyathocrinidae" — the Inadunata of our new classification — were 

 at that time principally founded, are interradials, which attained 

 their ventral position by being in lateral contact, in place of 

 resting laterally against the lower arm plates. The construction 

 of the ventral surface in the earlier Inadunata thereby became 

 fundamentally identical with that of the " Sphaeroidocrinidae," 

 except that the latter attained subsequently a larger number of 

 interradials. In the later Inadunata the ventral structure is very 

 different; indeed, so much so that the two sections according to 

 our former views should have been distinctly separated. This we 



