GENUS ECHINOCYSTITES. 317 



direction : the nodes of the lower range project a little beyond those 



above. Number and form of the summit plates not determined. 

 There is evidence of a central aperture, which is probably the mouth ; 



while at the upper lateral angles of two adjacent plates of the third 



series, and succeeded by a plate of the fourth series, is situated the 



ovarian aperture. 



The specimens examined are casts of the interior, some of which retain 

 parts of the test, and preserve in a greater or less degree marks of the 

 structure. 



Formation and locality. In the Racine limestone (Niagara group), 

 Racine, Wisconsin. 



The two following species I refer to the Cystidae with some hesitation, 

 notwithstanding the unsymmetrical form and peculiar character of one of 

 them, which closely resembles in its general features the Holocystites. 



In many of the Crinoidea proper, we find the plates arranged in succes- 

 sive order of one, two, or three following each other directly in what are 

 termed the radial series ; while between these rays are interradial plates 

 in the usual order of a larger one below, which supports two plates in the 

 second range, followed by a like or greater number in the third range. 



In the Cystideans of the described genera the plates do not follow this 

 order of arrangement, and cannot be separated into radial and interradial 

 series, according to the usual mode in Crinoidea. In the Cystideans, where 

 there are a considerable number of plates, they are arranged in alternating 

 order, so that each succeeding range above the second have their lower 

 margins more or less pointed and inserted partially between and resting 

 upon the sloping upper faces of those of the preceding range. This feature 

 is seen conspicuously in Holocystites, where the plates are numerous. 

 It sometimes happens, that owing to a curving form the plates follow each 

 other in direct order. 



Among the specimens- which I had provisionally placed among the Ho- 

 locystites is a small species of unsymmetrical, subclavate form, having 

 the two lower ranges of plates alternating as in that genus, while above 

 these the plates are arranged in consecutive order, until we reach the last 

 range, where every alternate one is omitted, thus producing a contraction 

 of this part. 



Since this form cannot be consistently referred to any described genus, 

 I propose the name Crinocystites. 



GENUS CRINOCYSTITES ( nov. gen.). 



Body elongate, composed of plates of subequal size. The number of basal 



plates undetermined. These support five hexagonal or heptagonal plates in 



the second range, and upon the upper edges of these, three plates of sinii- 



IJ 



