250 PROCEEDINGS OF THE ACADEMY OF [1881. 



1858. PI. tuberosus Hall. (^col. Rep. Iowa, i, pt. ii, p. 534, PI. 8, figs. 7 a, b ; Meek 

 and Worth., 1806, Pleuroor. tuberosus, Ueol. Rep. 111., ii, p. 172. Upper 

 liiirlini;toii limest. Burlington, Iowa. 



1849. PI. vesiculus McCoy. Ann, and Mag. Nat. Hist., p. 246. Mount, limest. 



Derbyshire, Eng. 

 1875 (?). PI. vexabilis White. Wheeler's U. S. Survey, West of LOOth merid., iv, 



Pal. p. 81, PL V, fig. 2. We doubt if this is a Platycrinus. 

 1858. PI. Wortbeni Hall. Geol. Rep. Iowa, i, pt. ii, p. 530, PL 8, fig. 4. Burlington 



limest. ]>urlington, Iowa. 



1850. PI. Yandelli Ow. and Sh. Jour. Acad. Nat. Sci. Phila. (new ser.), ii, pt. i; 



also U. S. Geo*. Surv. Iowa, Wise, and Minn., p. 537, PL 5 A, figs. 6 a, b. 

 Lower Burlington limest. Burlington, Iowa. 



Subgenus EUCLADOCRINUS Meek. 



1871. Meek. Hayden's Rep. U. S. Surv. of Terr., p. 373. 

 1878. Wachsm. and Spr. Proc. Acad. Nat. Sci. Phila., p. 243. 



Syn. Platycrinus White, in part. Proc. Bost. Soc. Nat. Hist., p. 17. 



The name Eucladocrinus was proposed by Meek in 1871 

 (Hayden's Rep. U. S. Survey of the Territories, p. 373) to desig- 

 nate a subgeneric group under Platycrinus^ of which PL pleuro- 

 viviinus White is the t3^pe. 



In the structure of the calyx, this form presents no apparent 

 difference from Platycrinus^ and it embraces species with a low, 

 broad cup shaped, and with an elongate body. It is characterized, 

 however, by having the radial series of the body, both dorsal and 

 ventral, greatly extended in the form of tubular free rays, which 

 bear the arms alternately on either side throughout their entire 

 length. These rays, in all the known species, divide on the second 

 radial into two branches, which remain joined by their inner sides 

 for the length of three or four plates, after which they beoorne 

 free, giving two free branches to each ray, or ten in all. A tubular 

 passage, arched over by the extensions of the vault, runs the whole 

 length of the rays, and these tubes, after uniting on the inside of 

 the second radial, connect with the visceral cavity. 



The arms are composed of a double series of interlocking 

 joints, and bear slender, single-jointed pinnules. 



This type bears the same relation to Platycrinus that Stegano- 

 crinus does to Actinocrinus^ and Melocrinus to Mariacrinus ; 

 and the two are ver^" closely connected by transition forms such 

 as PL prsenuntius, in which the free ray structure is clearly begun, 

 the radial areas being produced to the extent of ten or twelve 

 plates. 



