MORPHOLOGICAL PAET. 43 



cirri, although they may be arranged singly at wide intervals, are located 

 radially in dicyclic Crinoids, and interradially in monocyclic ones. This is 

 readily perceived on pentangular stems, in which the cirri rest within the 

 retreating angles of the joints, so as to alternate with the salient angles, and 

 hence are in line with the salient angles of the axial canal. 



The length of the cirri among Camerate Crinoids was very variable, and 

 they were in some species quite formidable. We have in our collection a 

 fragment from the lower part of the stem, apparently of Batocrimis grandis 

 (Plate I., Fig. 2), measuring 11 cm. in length, and tapering from a diameter 

 of 10 mm. at one end to 7 mm. at the other. It gives off numerous cirri, of 

 which those of the thicker or upper end are but little thinner than those of 

 the lower. Three of the lower cirri are preserved to a length of 16, 15^, and 

 15 cm. respectively, and may have been much longer, as they taper but 

 little, still having at their ends a thickness of 2^ to 3 mm. Five other cirri 

 are broken at a length of from 11 to 37 mm., and eight consist of only two 

 to ^\e joints ; while the sockets of three others are empty. The sockets are 

 deeplj^ excavated, and extend to nine joints, the surface being radiated. The 

 distal faces of the joints are slightly concave, the proximal joints shorter than 

 the distal, and the central perforation is round and of moderate size. Two 

 of the cirri in this specimen have a remarkable cyst of 14 to 18 mm. in 

 length by 9 mm. greatest width, one forming the distal end of the longest 

 cirrus, the other commencing about 8 mm. from the stem. The two thickest 

 joints in the inflated part of the one are nearly 4 mm. long, while the length 

 of the joints above and below the inflation does not exceed IJ mm. Similar 

 cysts are frequently found along the stem, but have not before been ob- 

 served to occur on the cirri. They resemble the Myzostoma cysts, which 

 occur along the arms of recent ComatulaB, and like them were evidently 

 caused by parasites. 



In another stem fragment from the Upper Helderberg of Louisville, Ky., 

 every joint is cirrus-bearing, and most of them have five large cirri — some 

 four or three — which almost touch those above and below. The cirri are 

 preserved to a length of 35 to 40 mm., and were probably much longer 

 (Plate L, Fig. 3). 



The cirri of the Actinocrinidae generally extend to one third the height of 

 the stem. They vary greatly in size, and are arranged at rather wide inter- 

 vals. The same structure probably prevailed in the Ichthyocrinidse, at least 

 in OnychocrinuB and Taxocrimis ; while in the Calyptocrinidae cirri occur only 



