THE FOSSIL CRINOID GENUS DOLATOCRINUS AND ITS ALLIES, 



bulging is due to the great enlargement and asymmetrical swelling 

 of the intestine, which nevertheless discharges from the tegmen 

 almost centrally, through a small anal tube. The interbrachials are 

 few in number, consisting of one large plate, which may be followed 

 by one or two in the succeeding ranges, flanked by other plates 

 resembling interbrachials, but which are in fact fixed pinnulars; 

 interpinnulars sometimes present. The anal side is differentiated 

 in the tegmen by a median row of large plates, and sometimes in 

 the dorsal cup by an extra plate in the second interbrachial range, 

 but this is not constant; a narrow linear series passes up to the 

 median row above mentioned. 



The base, in the left posterior position of the small plate, is not 

 only different from that of the associated genera, but is a departure 

 from the rule in monocyclic crinoids generally, this exceptional orien- 

 tation being known only in some specimens of Storthing ocrinus , and 

 the Recent genus, Hyocrinvs. This character is nearly constant 

 in both species. 



The condition of the first primibrach is also exceptional and pe- 

 culiar. Instead of being absent, as in Stereocrinus and Hadr ocrinus, 

 it is reduced to a small lunate or elliptic plate, occupying a curved 

 socket cut out of the distal face of the radial (or also out of the plate 

 above it), usuall}' less than the width of that plate, but sometimes 

 extending entirely across it. A similar irregularity has been observed 

 in Eucalyptocrinus rosaceus, from the Devonian of the Eifel, in which 

 the first primibrach is also sometimes entirely absent. 



The secundibrachs are arched into strongly rounded rays, with 

 broad depressions between. They form a continuous series which 

 pass into 10 strong, free, uniserial arms. They are incorporated in 

 the calyx to a varying extent by means of fixed pinnules, the bases of 

 which are closely united by suture. The lower secundibrachs follow- 

 ing the first bear a single pinnule, on the outside and inside of the 

 dichotom successively, while IIBr^, and probably all succeeding 

 brachials bear pinnules on both sides, increasing in number until 

 there are two on each side. This bipinnulate or quadripinnulate 

 structure is also unusual, but I have other good examples of it in the 

 genera Carpocrinus and Lampterocrinus. Ambulacral covering plates 

 in double series extend to near the base of the anal tube, and pinnular 

 ambulacra are also present, as in Marsipocrinus. These pinnules 

 give rise to openings through the calyx wall between the bases of the 

 rays, such as have been noted in species of Dolatocrinus , Batocrinus, 

 and other genera, in which they were formerly interpreted as "respi- 

 ratory pores." I have already explained their nature and origin 

 in the memoir on the genus Scyph ocrinus, 1917, (pp. 40-46). 



In the great preponderance of the ventral portion of the calyx, as 

 evidenced by the flattened dorsal cup and high tegmen. this genus 



