6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. "6 



arms themselves have not been seen in this genus. The cup is usu- 

 ally more or less elliptic, and all known specimens are small, the 

 maximum not exceeding ii mm. long diameter. 



Of the pair of small radials abreast, one has usually at its distal 

 face to the left a small tooth like elevation, which from analogy of the 

 structure in Catillocrinus we know to be connected with the anal plate 

 and tube. This determines the orientation of the calyx, the radial 

 last mentioned being the right posterior, its fellow small one the 

 right anterior, and the third small one. at the opposite side of the 

 cup the left anterior ; while the two large radials are the anterior and 

 left posterior respectively. This orientation was not observed in 

 some of the earlier descriptions and discussions {e. g., Wachsmuth 

 and Springer called the two large plates " antero-lateral "), which 

 fact must be remembered when comparing them with later statements. 



At the perimeter of the upper face of the radials, one opposite to 

 each food groove, are certain slit-like openings, which perforate the 

 plates and pass downward to the basal ring. Their continuation may 

 be seen at the margin of the five-sided pyramidal upper face of the 

 basal knob, of which I have a detached specimen (pi. i, fig. 9). Con- 

 sidering the great asymmetry which prevails in the parts above, it 

 is remarkable to find in this face a perfect pentagonal symmetry, the 

 openings apparently entering it in regular clusters of three. Schultze 

 describes them as twelve in number, three each in two of the sides 

 and two each in three ; but my specimen indicates that there is probably 

 one for each arm. 



These openings are for the lodgment of the dorsal nerve cords, 

 which lie back of, or below, the other nerves connected with the food 

 grooves, and proceed from the aboral motor nerve system. Usually 

 they lie in the brachial groove itself, but sometimes, as in this case, 

 they are lodged in a separate axial canal, which perforates the radial 

 facet into the substance of the plates, where it divides and branches 

 to the basals, passing ultimately into the chambered organ. Such 

 perforation of the radials is common in the recent crinoids, and occurs 

 in several Devonian genera, but is not often seen in other paleozoic 

 crinoids. In Mycocrinus the canals apparently pass downward di- 

 rectly through the radials and concentrate in the basal knob. But 

 in Catillocrinus, which has no such knob, they follow just under- 

 neath the food groove for some distance, separated from it by a thin 

 partition (pi. 2, figs. 10, ii, 12), and then turn downward, passing 

 into the usual branches and commissures too minute to be traced in 

 the fossils. 



