14 BULLETIN 115, UNITED STATES NATIONAL MUSEUM. 



the few massive appendages of the H. discus. It is in this respect 

 strikingly similar to Strotocrinus, which with a greatly expanded 

 calyx has similar small arms, in accordance with the fact, frequently 

 observed in crinoids, that increase in size of calyx is often accompa- 

 nied by a diminution in size of the arms. 



The interbrachial plates are few and large, usually in three ranges 

 of 1 — 2 — 1 in the interray, and 2, exce])tionally 3, in single series in 

 the second axils, with an occasional plate in the third. The anal 

 interradius has usually an extra plate in the second range, but this 

 ma}' sometimes also occur in other interradii, so the differentiation 

 is not certain. 



The column of this genus partakes of a peculiar structure, more 

 fully to be described under Dolatocrinus, whereby the nodal colum- 



nals are remarkably conspicuous, having a 

 flanged peripheral rim overhanging and some- 

 times concealing the adjoining internodals, 

 and being studded in varying number with 

 projecting cogs resembling fins, while the in- 

 ternodals are thin and of less diameter. 



Fig. 6.— Distribution of arms a ii j.1- • • i j* ™ . oo u 



IN HiMERocRiNus ^^ ^^^ spccimeus, mcludmg some 23 show- 



ing the basal cone only, in addition to the 

 20 above mentioned, seem to belong to the type species, with the 

 possible exception of one. "Hall's Coronocrinus, from the Manlius of 

 New York, should be compared with this genus. 



Horizon and locality. — The type and only described species is from 

 the Onondaga (Jeffersonville) limestone, at Louisville, Kentucky. 



Genus TECHNOCRINUS Hall. 



TECHNOCRINUS NIAGARENSIS, new species. 



Plate 5, figs. 1, 2. 



Among collections made for me in western Tennessee in recent 

 years are two forms belonging to the group under consideration, the 

 occurrence of which carries the age of their genera back to earlier 

 epochs than hitherto known. TecTinocrinus is typically an Oriskany 

 fossil of the Lower Devonian, found heretofore only in Maryland 

 and New York. It must now be credited also to the Silurian, on 

 the evidence of the single specimen which I have figured under the 

 above name. It was found in place in the Bob formation of the late 

 Niagaran in the first bluff below Cerro Gordo, on the left side of the 

 Tennessee River, in Hardin County, Tennessee; and it was associated 

 in the same layer with Lampterocrinus, which is a thoroughly charac- 

 teristic Niagaran form. The specimen is in good condition, showing 

 aU the generic characters very distinctly, and in addition to these the 

 plates of the dorsal cup are surmounted by small, delicate spines, some 



