1884.] NATURAL SCIENCES OF PHILADELPHIA. 145 



basals in its axis, which is governed by the anal. Plates five, 

 three small and two large, of subequal sizes ; upper portion 

 incurved so as to form part of the brim of the dome ; deeply ex- 

 cavated above in the incurved portion, with dove-tailed notches 

 to receive the brachials; first two radials on the posterior side 

 small, resting on the sloping sides of the anal and the posteriorly 

 expanded portion of the next radials ; lateral radials much elon- 

 gated, so as to rest upon the basals ; and have the elongated 

 portion much expanded, especially anterioi'ly, where they meet 

 under the anterior radial : anterior radial small, supported by the 

 lateral radials upon their expanded portion, which in the dextral 

 one is supported by three basals like the anal, while the other 

 rests on the two wider pentagonal basals and consequently has 

 an acute inferior angle instead of a truncate one. 



This anomalous genus should probably be placed next to 

 Eyhocrinus with which it has some slight affinity. 



So far found only in the Clinton Group. 



Triacrinus pyriformis (n. sp.). PI. Ill, fig. 1. 



Calyx small, subpyriform. 



Base broad, truncate, with a slight, flat, wide depression to 

 receive the column which was here evidently about as broad ; 

 leaving only a fine sharp projecting marginal ring. 



Height to width as three to two. 



Basals medium; first to the right of anal; acutely pentagonal, 

 height and width about equal ; the quadrangular plates are about 

 one-half as high as the pentagonal ones ; height to width as one 

 to two ; the two adjoining pentagonal plates are as high as the 

 other, and are wider than high ; extending nearly half way around 

 the basal ring. 



Second ring equally triehotomous. Anal large, slightly wider 

 than high. 



First two posterior radials medium, obversely equiform with 

 their lower and external lateral sides curving outwards ; lateral 

 large radials slightly expanded posteriorly and widely anteriorly ; 

 anterior radial equilateral, with lateral angles fitting into the 

 expanded radials upon which it rests. The wide dove-tailed 

 incisions to receive the brachials are about two-thirds as wide as 

 the upper part of the plates, at their lower expanded portion ; 

 above which point the upper part of the plate is rather abruptly 



