334 PROCEEDINGS OF THE ACADEMY OF [1879. 



but in all cases, so far as known, low down and situated laterally, 

 not posteriorly. 



Dome constructed like that of Cyathocrinus. Apical dome 

 plates frequently pushed toward the front by the large ventral sac. 



Column round or pentagonal, composed of thin joints with a 

 small central aperture. 



Geological position, etc Poteriocrinus has not been found in 

 the Silurian, neither in this country nor in Europe; the few species 

 which were recorded from that age having since been referred to 

 Dendrocrinus, Homocrinus, etc. It nourished to some extent in 

 the Devonian, but reached its climax both in variety of form and 

 number of individuals in the Subcarboniferous. There are known 

 IT species from the Devonian and 99 from the Subcarboniferous, 

 of which 21 are from Europe and 89 from America. The species 

 are arranged under the respective sections as follows: 



A. Typical form. 



Cal}'x obconical, plates delicate, with elevated wrinkles or radi- 

 ating plications. Kadials with a semicircular scar facing outward, 

 and deeply notched, not filling the full width of the plate. Bra- 

 chials one by five, long, laterall}- constricted in the middle. 

 Sutures somewhat gaping. Arms long and brandling. Ventral 

 sac very long and hea\ r 3 r . Column round. 



1866. Poteriocrinus angulosus SchuHze. Echinod. Eifl. Kalk., p. 50, pi. 5, figs. 



3, 3 a. Devonian. Eifel, Germany. 

 1821. Poteriocr. crassus Miller. (Miller's type of the genus.) Nat. Hist. Crin., 



p. 68, with figures; Schlottlein, 1822. Nachtr. Petrefactenkunde, vol. i. 



p. 82; Id., vol. ii. p. 93, pi. 25, fig. 2; Blainville, 1834. Mon. de Actin., 



p. 260, pi. 29, fig. 1 ; L. Agassiz, 1835. Mem. de la Soc. de Neuch., vol. i. 



p. 197; Milne Edwards, 1836. Lamarck's Anim. s. vert., 2d ed., vol. ii. p. 



664; DeKoninck, 1842. Desc. des Anim. Foss. du Terr. Carb., p. 46, pi. F. 



fig. 4; Austin, 1843. Rec. and Foss. Crin., p. 69, pi. 8, figs. 3 a-k, and pi. 



9, fig. 1 ; De Koninck and Lehon, 1853. Recherch. s. les Crin. Belg., p. 97, pi. 



1, fig. 10 a-d. Subcarb. Yorkshire, England, and Vise, Belgium. 



It is very doubtful whether specimens figured by these various 

 authors represent the same species. De Koninck refers Austin's 

 figures, pi. 8, fig. a-f and pi. 9, fig. 1, to Pot. spissus, while he 

 himself figures a specimen which very probably belongs to Bary- 

 crinus. See our remarks on the genus. 



*1861. Poteriocr. doris Hall. (ScapMocr. doris.) Desc. New. Pal. Crin., p. 7, 

 Bost. Journ. Nat. Hist., p. 310. Upper Burl, limest. Subcarb. Burling- 

 ton, Iowa. 



