162 CRINOIDS. 



preceding group. Although never taking a prominent part in 

 the fossil faunas, they are, from a morphological standpoint, 

 perhaps the most important of any. And while probably none 

 of the forms now known actually represent the larvj© of the 

 ancient crinoids generally, some of them are certainly quite 

 embryonal in appearance. These furnish a clue to the true 

 explanation of many anatomical features in the other groups 

 which have, until recently, remained enigmatical. 



The third great section of the Crinoidea is a small and in- 

 conspicuous one, but nevertheless comprises many important 

 forms, which are peculiar on account of their singular ventral 

 structure, pliable test and non-pinnulate arms. To the fourth 

 grand group belong most of the modern feather-stars. 



Glyptocrinus fornshelli Miller. 



Gluptocrinus fornshelli Miller, 1874 : Cincinuati Quart. Jour. Sci. , vol. I, 

 p. 318, fig. 41. 



This singular and beautiful form has been recognized in 

 Missouri by a few single plates with their unique ornamenta- 

 tion. 



Horizon andlocality — Silurian, Hudson shales: Louis- 

 iana. 



Ptychocrinus splendens (S. A. Miller). 



Plate xxii, fig. 1, 



Gaurocrinus splendens Miller, 1883: Jour. Cincinnati Soc. Nat. Hist., vol. 



VI, p. 230. 

 Ptychocrinus splendens Wachsmuth & Springer, 1885: Proc. Acad, Nat. 



Sci., Phila., p. 323. 



Crown very similar to that of Olyptocrinus, but differing 

 in having well-defined- infrabasals. The radials and calycinal 

 brachials have a prominent median ridge, which merges into 

 the free arms. 



Horizon and Locality. — Lower Silurian, Trenton limestone : 

 Cape Girardeau. 



Rhodocrinus wortheni ( Hall). 



Rhodocrinus wortheni Hall, 1858 : Geol. Iowa, vol. I, p. 556, pi. ix, figs. 8a-c. 



Calyx globular, slightly flattened dorsally. Infrabasals 



five, small, usually covered by the stem. Basals five, rather 



large. Radials rather large; costals slightly smaller. Arms 



