322 PROCEEDINGS OF THE ACADEMY OF [1885. 



with Hall's Glyptocrinus parvus, which, evidently, according to 

 Hall's figure (but not Meek's), has the same characters. 



We cannot agree with Miller that Wetherby's Reteocrinus 

 gracilis, in which ill-formed interradials separate the radials down 

 to the base, and in which the basals are squarely truncated above 

 and form the base of the interradial spaces, is a synonym of 

 Glyptoa-inus angularis, in which the " interradial spaces have a 

 hexagonal plate resting between the upper sloping side of the 

 first radials." 



The three species differ from all established genera of this 

 family in having their arms constructed of single joints. It 

 might, perhaps, be doubted whether this is a good generic 

 character, as all Crinoids with double-jointed arms are single- 

 jointed in their younger stages ; but finding three species with 

 the same kind of arms, and these comprising the only known 

 Lower Silurian species of this family, we are evidently justified 

 in making it a generic distinction. 



Generic Diagnosis. — In general form closely resembling Ghjp- 

 tocrinus. Radials with a fold-like, strong, tubular ridge along 

 their median line ; interradial spaces depressed. 



Underbasals five, well shown in a side view. Basals five, large ; 

 all of them hexagonal. Primary radials 3X5; the first ones 

 heptagonal, but the upper sloping sides facing the azygous side 

 longer, forming a deep notch for the reception of a very large 

 anal plate. Secondary radials three or more, which have the 

 appearance of arm-plates, and gradually pass into free joints. 

 They have strong arm-like pinnules, given off from alternate 

 sides. 



Interradials consisting of one plate in the first row, two in the 

 second, and three in the third row. The azygous side wider ; the 

 first plate extending far down between the first radials, sometimes 

 touching the basals, and there are three in place of two plates in 

 the second series. Structure of the ventral side unknown. 

 Column small ; cylindrical. 



*1879. Ptychocrinus angularis (Miller and Dyer), Glyptoor. angularis, Journ. 



Cinoin. Soc. Nat Hist., p. 5, PI. 1, fig. 10. — 1883, Gaurocr. angularis S. A. 



Miller, Journ. Cincin. Soc. Nat. Hist., vol. vi, p. 229. — Hudson River gr. 



Cincinnati, Ohio. 

 *1872. Pt. parvus (Hall), Glyptocr. parvus, Desc. New Crin., etc., PI. 1, fig. 17 



I without description), 24th Rep. N. Y. State Cab. Nat. Hist., p. 207, PI. v, 



fig. 17; (?) Meek, 1873, Geol. Rep. Ohio, Pal. i, p. 36, PI. 2, figs. 4ab; (?) 



