244 PALEONTOLOGY OF NEW-YORK. 



plates, and tlie larger tubercles sometimes forming straight ridges from the centre to the angles 

 of the plates. 



This exquisitely beautiful little fossil is from the collection of Col. Jewett of hr 1-nort, and 

 was found associated with the preceding species, and with Caryocrinus ornatus. Tlus is much 

 smaller than Callocystites, and is very conspicuously different in the form of the plates and 

 the number of those in the second series, as well as in the position of the higher peciiuattJ 

 apertures. The arms are but four, and very obviously consist of an anterior and posterior pair, 

 which are united at their bases. The character of the shallow groove in which these arms rest, 

 and the groove or avenue in the arms themselves, is precisely similar to the preceding genus. 

 The little ossicula partially filling this groove are not perfectly preserved in that one, though 

 there remains sufficient to prove their existence originally. In the present form there is an oral 

 orifice near the summit, and a minute anal pore below ; while in Callocystites the mouth is 

 smaller, and the anal orifice proportionally larger, and there is a distinct tubercle on one side 

 of the mouth, which does not appear in this one. 



The body, in a well preserved specimen, appears to be slightly compressed laterally ; though 

 in another specimen, apparently in its natural condition, there is no perceptible difference in the 

 two diameters. The groove in which the arms lie is more deeply impressed near the summit 

 than in the lower part, and distinctly divides the body into four lobes. Modifications of the 

 form, to some extent, take place from the introduction of supernumerary plates as in the crinoids 

 proper. This also modifies the form of the adjoining plates, as in the example fig. 5, where the 

 introduction of a quadrangular plate between the first and second series has truncated an angle 

 of one of the pentagonal basal plates, and changed the form of one, and altered the relative 

 position of the other adjoining plate, of the two succeeding ones of the second series. Modifi- 

 cations in the form, and subdivision of plates in the third and fourth series, appear not to be 

 uncommon in this species. 



The largest specimens seen reach the size of the figures on Plate 51, though others are 

 smaller. 



Fig. 1. The posterior side, showing the ovarian aperture, the shallow groove in which the arms 



are lodged, and the base of the larger tentaculum. 

 Fig. 2. The left side, showing the pectinated apertures and arrangement of plates on that side. 

 Fig. 3. The right side, showing the pectinated apertures and the protruding plates of the ovarian 



pyramid. The plates of one of the arms remain, retaining the minute ossicula, which 



are shown diverging into the lobes of the groove to the base of the tentacula. 

 Fig. 4. The anterior side, showing the pectinated apertures at the base, the grooves for the 



anterior pair of arms, and the base of the large tentaculum at the summit. 

 Fig. 5. Diagram showing the structure of one specimen having an intercalated quadrangular 



plate between the first and second series of plates. 

 Fig. 6. Diagram of the structure of another specimen, where there are only the usual number 



of plates in the first and second series. One plate of the third series, over the ovarian 



aperture, is divided into three distinct pfetes. Between the plates bearing the pec- 



