1886.'] NATURAL SCIENCES OF PHILADELPHIA, 151 



ARACHNOCRINUS M. and W., Rev. I, p. 92. 



In our former list we erroneously placed Poteriocrinus |)m- 

 formis Roemer under Arachnocrinus. From specimens which we 

 obtained lately in western Tennessee, and in which the azygous 

 side and also the brachials are preserved, we are convinced that 

 it is a Lecanocrinus. 



GISSOCRINUS Angelin, Rev. I, p. 89. 



ACHRADOCRINUS Sclmltze. 



1879. Zittel, Handb. d. Palaeont,, i, p. 364. 

 1866. Schultze, Ecliin. Eifl. Kalk., p. 101. 



Schultze in defining this genus thought it to be closely allied 

 to Gasterocoma, and Zittel and de Loriol place it among the 

 Gasterocomidoe. In our opinion, the similarity between Gastero- 

 coma and Achradocrinus is more superficial than real. Gastero- 

 coma has five underbasals, and the column in addition to the 

 axial canal is provided with four peripheral vessels, which are 

 altogether unrepresented in the other form. The two agree only 

 in the position of the anal aperture. The affinities of Achrado- 

 crinus are much closer with Sphaerocrinus, from which it differs 

 only, as far as known, in the position of the anal plate. 



Generic Diagnosis. Dorsal cup deeply cup-shaped ; symmetry 

 decidedly bilateral. Underbasals five, equal, of medium size, 

 extending beyond the column, and visible in a side view. Basals 

 five, four of them angular above, the posterior one truncate, and 

 supporting an anal plate. Radials all meeting laterally, three of 

 them equal ; the two postero-lateral ones deeply excavated for the 

 reception of the anal plate, which they inclose on three sides by 

 meeting above. The radials are slightly notched at their upper 

 margin, and have upon the outer side of the plate a narrow, 

 horseshoe-like articular facet, pierced by a small dorsal canal, 

 which is located at some distance from the notch. At the azj-gous 

 side there is only an anal plate, which is subquadrangular, its 

 lateral margins arched, its upper face narrower and excavated for 

 the ventral sac, which is cylindrical and placed between this plate 

 and the lateral extensions of adjoining radials. The tube has a 

 ventral position owing to the strongly inflected upper portions of 

 the radials. Arms unknown. Column circular ; with a small 

 central canal. 



The only known species is : 



1866. Achradocrinus ventrosus Schultze, Echin. Eifl. Kalk., p. 101, Pi. 12, fig. 6. 

 Devonian. Eifel, Germany. 



