CESTOCRINUS KIRK 223 



mutely equivalent horizons elsewhere, the form must be exceedingly 

 rare. The lack of a known antecedent form in the great crinoid 

 collections of the Burlington is significant. 



CESTOCRINUS STRIATUS. new species 



Plate 31 



The description is based on a ])erfect dorsal cup with the arms 

 preserved in part to a length of 10 mm. and with about 25 mm. of 

 column attached. The proximal portion of the ventral sac is also 

 present. The specimen has been freed from the matrix. 



The dorsal cup is narrowly companulate in form and composed 

 of fairly thin plates. The surface of the plates is finely papillose, 

 the papillae tending to become confluent in linear series, thus forming- 

 striae normal to the faces of the plates. Low folds pass from radial 

 to radial, radials to basals, and basals to infrabasals. The dorsal 

 cup has a height to the arm bases of approximately 15 mm. and an 

 average maxinuim diameter of about 14 mm. 



The IBB are five in number, pentagonal in outline, with an aver- 

 age height of 4.3 mm. and an average maximum breadth of about 

 5 mm. The BB. w^ith the exception of the posterior, are hexagonal 

 in outline, having an average height of T.3 mm. and an average 

 maxinuim breadth of 6 mm. The posterior basal is octagonal in 

 outline and has a height of 11.3 mm. and a maximum breadth of 

 7.8 mm. The distal point of the post B lies at approximately the 

 plane of the arm bases. On its distal sloping faces the post B sup- 

 ports the two proximal tube plates. The RR are relatively small, 

 having an average height of 5.2 mm. and an average maximum 

 width of 6.3 mm. The arm facets are horseshoe-shaped, approxi- 

 mately one-half the width of the radials at that level, and stand 

 out sharply above the surface of the plates. 



The arms are proportionally slender and composed of relatively 

 long, subcylindrical brachials. The primibrachs have an average 

 width of 2.C) nun. In the r ant R there are four IBr and in the 

 1 ant R three IBr. In the ant R four IBr are shown without an 

 axillary, which folloAvs the common rule among inadunate crinoids 

 that the ant R tends to carry more primibrachs than the other rays. 



The ventral sac, judged from the proximal portion preserved. Avas 

 subcylindrical in shape, proportionally slender, and composed of 

 rather large, heavy plates. The proximal tube plates are very large, 

 that to the right having a height of 7.5 mm. and that to the left 6.5 

 mm. The tegmen was composed of a flexible integument of small 

 nodose and rugose plates. 



