228 PROCEEDINGS OF THE ACADEMY OF [1885. 



known genera, and all have interradials, by means of which fre- 

 quently a large series of arm plates are incorporated into the 

 calyx, and thereby elevated to the rank of radials. The term 

 "calyx," although applied sometimes in a general way to the 

 whole skeleton exclusively of arms and column, has been of late 

 restricted to the dorsal cup, and all structures upon the ventral 

 surface were called variously vault, dome or disk. It has been 

 the general opinion that all plates located ventrally, in analogy 

 with the Neocrinoidea, either were perisomic, or at least formed a 

 part of the actinal system. This is the view expressed by Car- 

 penter in the Challenger Report, and we must acknowledge it 

 was our own until quite recently. We now hold that a large part 

 of the ventral surface, throughout the Palaeocrinoidea, was covered 

 by abactinal plates, and that the calyx extended to the summit 

 pieces, the so-called " apical dome plates." In this sense the 

 term " calyx " will be used by us in this part of the Revision, 

 while the plates beneath the free arms comprise the " dorsal cup." 

 We further use the term " ventral disk " exclusively to denote the 

 upper surface of the visceral mass, in which the mouth is situated, 

 and from which the food grooves radiate outward. The " disk " 

 is clothed by the " perisome," which may be exposed to view or 

 subtegminal, simply membranous or studded with plates ; if sub- 

 tegminal, it is covered by the " vault," which may be rigid or 

 pliable. 



The name " Camarata " is proposed for all Palaeocrinoidea in 

 which the lower arm plates are incorporated into the calyx by 

 interradial plates, and in which all component- parts of the test, 

 dorsally and ventrally, are solidly connected by suture. 



Under the name " Articulata " we include those families in 

 which the plates of the test are united by loose ligaments or 

 muscles, and in which they are somewhat movable. 



The name u Inadunata" is proposed for all Palaeocrinoidea in 

 which the arms are free above the first radials and which have 

 five single interradials, located ventrally. 



These groups will be better defined at the proper place. 



A. The Basals and Underbasals. 



The basals are represented in the Palaeocrinoidea by one or two 

 rino-s of plates. The basals proper constitute the first ring beneath 

 the radials ; the second or proximal ring contains the underbasals. 



