1886.] NATURAL SCIENCES OF PHILADELPHIA. 97 



not three ; but in one of those species the basals are so small that 

 they were almost completely covered by the column, and it appears 

 as if the sutures between the plates of the second ring, of which 

 only three touch the basals, were the sutures between the plates 

 of the first ring. A similar structure is found in Pisocrinus 

 pilula (Iconogr., PL 4, fig. 4 6), a species which in its general 

 aspect is closely allied to Triacrinus depressus MUller. We do 

 not pretend to say, however, that this species had five basals ; it 

 is very possible that two of these plates became anchylosed, and 

 that the genus made its reappearance in the Devonian with only 

 three basals. 



Generic Diagnosis. Calyx in its general aspect clove-shaped, 

 its form subconical, sometimes pyriform. 



Basals five, unequal; three of them larger and trapezoidal, the 

 two smaller ones trigonal, which combined form an irregularly 

 triangular cup. 



The radials are extremely irregular, only the two anterolateral 

 ones touching the basals. These two are more than twice as 

 large as the other three plates ; they are hexagonal, and have the 

 same form and size. The anterior radial is triangular, with con- 

 vex sides, and rests with its lower angle half way between the 

 two larger ones. At the posterior side, the basals do not support 

 a radial, but are succeeded by a pentangular azygous plate, which 

 shares with the two large radials an equal part. The plate has 

 the form of an axillary, is broadly truncate below, with short 

 lateral faces, and is sharply angular above. The two postero- 

 lateral radials meet above the azygous plate, resting upon its 

 sloping upper sides, and against the upper half of the two larger 

 radials. Their width is identical with that of the larger ones, 

 and in a ventral aspect the radials appear to be perfectly 

 sj^mmetrical. 



Pisocrinus has similar articular appendages as Symhathocrinus, 

 which cover a good part of the ventral surface. The articula- 

 tion, however, does not occup}' the whole width of the radials; 

 there is at each side of the plates an upright extension, which 

 together with that of adjoining radials produces interradially, 

 between the arms, a conspicuous projection, similar to that of 

 Haplocrinus^'but more prominent. The construction of the ven- 

 tral side is not known, the space beyond the articular faces is 



