PLATE IV. 



Fig. 1. Platycrinites gigas, a to c. 



1. a. — specimen shewng the perisomic ray-bearing j^late, A\ith the base of ray attached. 

 1. h. — lateral aspect of specimen, exhibiting the meso-plate with its central tubercle, the 



abdominal plates, &c. 

 1. c. — dorso-central aspect. 



Fig. 2. Platycrinites rugosus. 



2. d. — dorso-central aspect, also exliibiting the basal joints of the rays. 



2. e. — ^lateral aspect of specimen, shelving the excavations for the rays. 



2. f. — ^lateral aspect of a specimen, exhibitmg portions of the rays, &c. 



2. g. — ^lateral aspect of a variety of the rugosus. 



2. h. — dorso-central aspect of the same variety. 



2. i. — dorso-central aspect of another and smaller variety. 



2. k. — lateral aspect of the last named variety. 



Fig. 3. Platycrinites tuberculatus. 



3. m. — lateral aspect, exhibiting the lateral oral orifice between the rays, &c. 



3. n. — ^lateral aspect, shewing the excavations for the rays, tuberciilated plates, &c. 



3. 0. — dorso-central aspect. 



3. p. — dorso-.central aspect of a smaller specimen. 



3. q. — the apex of the same specimen. 



3. s. — dorso-central view of a variety with smooth perisomic jolates. 



3. t. — meso-plate. 



3. u. — small perisomic ray-bearing plate, exhibiting the excavation for the rays. 



X. — fragment of a column, with tlie sockets for the articulation of the auxiliary side 

 arms. 



y. — portion of column. These two columnar fragments are supposed to appertain to 

 the rugosus. 



In this plate the di'awings are all, with the exception of the columnar fragments el- 

 and y, taken from sjjecimens in the possession of the Bristol Institution. 



