190 PROCEEDINGS OF THE ACADEMY OF [1886. 



differs from that genus, however, in having no underbasals and no 

 stem, being simply attached by the basals. In its sessile state it 

 resembles the recent genus Holopus, with which it also agrees in 

 having an undivided base. 



Generic Diagnosis, etc. Sessile in its larval state ; free-floating 

 in the adult, being attached by tlie lower end of the basals. 



Basals unusually large, elongate, closely anchylosed so as to 

 show no suture lines at the outer face; internally, however, there 

 are indications that the base might have been bisected. In the 

 young animal the form of the base is irregular and linear, in the 

 adult subglobose or deeply bowl-shaped, and the scar by which 

 the animal was attached, becomes totally obliterated by heavy 

 deposits of calcareous matter. Owing to this deposit the outer 

 form of the base differs considerably from the form of the inner 

 cavity, which grows gradually narrower toward the bottom, and 

 frequentl}^ ends in a sharp point. The walls are massive at their 

 lower parts, thin at the upper edge, which shows six excavated 

 faces for the attachment of five radials and an anal plate. 



Radials comparatively small, quadrangular, articular facet but 

 slightly excavated, occupying the full width of the plates ; pro- 

 vided with a transverse articular ridge. The anal plate is in line 

 with, and has the length of the radials, but is narrower ; it sup- 

 ports a small plate, but beyond that nothing is known of the anal 

 apparatus. The structure of the ventral surface has not been 

 observed. 



The arms are broad at the base, composed of extremely' short 

 transverse pieces, of which ten or more occur between the first 

 bifurcation. Nothing is known of pinnules, nor of the condition 

 of the ventral furrow. 



Geological Position, etc. Edriocrinus occurs in the Helder- 

 berg group of America, in which portions of the basal cup are 

 rather abundant. 



1859. Edriocrinus pocilliformis Hall, Pal. Rep. N. York, iii, p. 121, PI. 5, figs. 8-12 ; 

 also 1868, Geol. Rep. Illinois, iii, p. 370, PI. 7, figs. 5 a, 6. Lower Helder- 

 berg gr. Albany, New York and Perry Co., Mo. 



1862. E. pyriformis Hall, 15tli Rep. N. Y. St. Cab. Nat. Hist., p. 116, PI. 1, figs. 23 

 and 24. Upper Helderberg gr. Utica, New York. 



1859. E. saoculus Hall, type of the genus. Pal. Rep. N. York, vol. iii, p. 143, PI. 

 87, figs. 1-22. Oriskany sand.st. Cumberland, Maryland. 



I 



