38 rLATYCIJINIU.E rLATYCRINrS. 



The Perisomic Plates. — The stiias on these plates radiate from tlie excavations for 

 tlie rays, wliich are exceedingly small, to the lateral and inferior edges; other faintly 

 marked striae cross the former in a clrcidar direction producing a slight reticulated 

 appearance on the plates. 



The Meso-Plates. — The exact shape of these plates is unknown ; the lower 

 portion is however angular and finely striated. 



The Abdominal Plates.^ — Unknown. 



The Mouth — Unascertained; apparently central. 



The Rays — Agree in number and mode of articulation with the typical species, but 

 they are more delicate and longer ui proportion to the size of the animal. 



The Tentacula — Are longer and closer than in the Isevis. 



The Column. — ^The column of this species was unknown to Miller, but we have 

 been so fortunate as to find several specimens with portions of it attached to the dorso- 

 central plate. It is subject to the same modifications of structure as the column of the 

 typical species. 



The Base of Attachment — Is unascertained. If the last described species is 

 entitled from its highly ornamented exterior to rank as the Queen of the Plalycrini, 

 the striatus equally demands our admiration for its delicate form and structure, in wliich 

 it equals or surpasses all others of the genus yet discovered. The peculiar 

 length and fineness of the tentacula, with the great delicacy of the rays make it an 

 object of particular interest to the admirers of graceful forms. The striatus is the 

 smallest and most delicate species of Platycrinus at present known, as evinced by 

 the size of its embedded remains. Of all the specimens hitherto discovered, that which 

 is represented in our third plate, figure 3. p. is supposed to be the largest and most 

 perfect. 



9. Species. Platycrinus Gigas. (Gilherlson.) 

 PL IV. fg. 1, a, h, c. 



Definition. — Dorso-central plate pentagonal and broad ; perisomic plates smooth and 

 wide ; meso-plates rather unequal in size ; abdominal plates large, with a central tubercle 

 on each ; mouth central, and very slightly produced. Rays and column unknown. 



