1881.] NATURAL SCIENCES OF PHILADELPHIA. 301 



This seems to us suflicient to separate the two forms, but in 

 other respects the relations with Dolatocrinus are so close, that 

 they justify only a subgeneric division, for which we propose the 

 following : — • 



Diagnosis. — Bod}' depressed ; calyx truncate up to the second 

 radials, the latter bending abruptl}^ and forming a low basin with 

 straight sides. Dome but sliglitly elevated, its interradial por- 

 tions depressed and deeply grooved toward the arm bases, giving 

 to the radial regions a certain prominence, and to the body, 

 viewed from the summit, a somewliat lobed appearance ; sym- 

 metry' strictl}' pentahedral. 



Basal disk small, scarcel}' projecting beyond the column, funnel- 

 shaped, composed of three closely anchylosed pieces. Primary 

 radials 2X5; the first hexagonal ; the second pentagonal, sup- 

 porting two radials of the second order, the latter supporting the 

 arms. So far as the specimens are preserved, there are only two 

 arm openings to each ray, these, however, are so large that they 

 may form the inner cavit}^ of free brachial appendages with 

 numerous arms. Arras entirely unknown. 



Interradials two, large, with several small plates above ; the 

 two former in series of one each ; the first the largest plate of 

 the body, heptagonal ; the second hexagonal, smaller than the 

 radial plates ; succeeding pieces placed within the depressions 

 between the arm bases ; anal side not distinct. 



Yault composed of a moderate number of medium-sized pieces ; 

 apical dome-plates easily recognized by their larger size. Anal 

 opening subcentral, extended into a tube. 



Column round ; central canal large, pentalobate. 



Geological Position, etc Upper Helderberg group of America. 



1878. Stereocrinus triangulatus Barris. Davenport A-.ad. Nat. Sei., p. 283, PI. 11, 



figs. 1, 2. Encrinal limest. Near Diiveiii>ort, Towa. 

 1878. Stereocr. triangulatus var. liratus Ban-is. Ibid. p. 284, PI. 11, firr. 3. 



Encrinal liu.est. Near Davenport, Iowa. 



cl. Pekiechocrinites. 



12. PERIECHOCEINTJS. Austin. 



1843. Austin. Ami. and Mag. Nat. Hist., x, p. 109 (no definition). 



1843. Austin. Ibid., xi, p. 203. 



1848. Morris. Cat. Brit. Foss. (ed. lst\ p. 56. 



1857. Pictet. Traite de Paleont., iv, p. 323. 



1878. Angel. Iconogr. Crin. Suec, p. 6. 



