34 SMITHSONIAN INSTITUTION 



In Forbesiocrimis, with large infrabasals, the rim rises from their inner 

 edges, and is triangular or trilobate in general outline, the apices resting medi- 

 ally upon the plates and coinciding with them in relative position (PI. XXX, 

 figs. 5c, 6c, etc.). The internal cavity of the funnel is divided into five 

 unequal channels continuous with those of the stem lumen; three large channels 

 are opposite the inf rabasal sutures ; while the two small ones are median upon 

 the large compound plates. With the three lobes of the funnel thus coinciding 

 exteriorly with the three unequal infrabasals, we would naturally expect the 

 same result as in Ichthyocrinus to be attained by division of the channels upon 

 the two larger lobes; but instead of that, by a most singular arrangement of 

 the septa (further described in the generic discussion under Forbesiocrimis), 

 five unequal interradial channels are produced which pass with that orientation 

 down into the stem (text-fig. 2a). The same three-lobed funnel accompanied 

 by interradial orientation of the stem lumen occurs in Taxocrinns and 

 Onychocrinus. 



In Lecanocrinus and Pycnosaccus, where the infrabasals take a distinct 

 part in the formation of the calyx wall, the tri-lobate funnel is also formed on 

 their inner floor, divided by the septa into five unequal channels; but here, 

 instead of the chambers as in Forbesiocrimis, it is the septa between the cham- 

 bers which coincide with the infrabasal sutures (text-fig. 3); therefore the 

 channels are radial in position, and pass into the stem with the same orienta- 

 tion as in Ichthyocrinus, but this orientation is attained by a different process. 



Thus there is an absence of uniformity in the orientation of the axial 

 canal, partly due to the presence of unequal infrabasals. In some cases of the 

 Forbesiocrimis type the lobes of the lumen appear doubtful in position, partly 

 radial and partly interradial, owing to the great excess in size of the three 

 larger ones. This irregularity is mostly corrected within a short distance down 

 the stem, where the lobes of the lumen are usually decidedly interradial, as 

 shown by figure 14 on Plate XXX. A somewhat similar variation in the posi- 

 tion of the stem lumen is seen in monocyclic Camerata with three basals. In 

 those it should be strictly interradial, but examination of a large number of 

 specimens shows that the orientation departs rather frequently from a per- 

 fectly regular position. It does not follow that the actual orientation of the 

 nerve cords in the stem was subject to these irregularities. 



The primary axial nerve cords proceed from the cavities or lobes of the 

 chambered organ which is lodged within the ring of basals in monocyclic, or of 

 infrabasals in dicyclic, forms. These cavities are prolonged downward into 

 the stem in five peripheral vessels which surround the central vascular axis. 

 These enlarge at the nodal ossicles, and from the nodal enlargements the cirrus 

 vessels pass out, following the line of junction of the pentameres of the stem. 

 Thus the orientation of the cirri, and of the peripheral canals with which they 



