328 PROCEEDINGS OF THE ACADEMY OP [1879. 



but it is fully sufficient for identification, as it affords the means 

 of separating this form from the only other genus of this family 

 then known. It gives us unquestionable evidence of the existence 

 of at least two anal plates within the calyx, which are plainly 

 shown in the diagrams ; while in Miller's typical species of Gya 

 thocrinus only a single anal plate is mentioned or figured, which 

 is wedged in between the scapulae or first radial plates. 



In the description of P. crassus, which is Miller's first species, 

 and ought to be the t3 7 pe of the genus, he gives additional infor- 

 mation regarding the scapulae or radials. They are described as 

 thin plates, obliquely truncated at the upper margins, excavated 

 with a horseshoe-like impression occupying scarcely more than 

 one-third the width of the plates. Miller's second species agrees 

 well with the preceding. It has only one brachial, which is a 

 bifurcating plate, narrow, four to five times longer than wide, 

 supporting an arm on each side. Only one arm is preserved 

 which has the same dimensions as the brachial, and a deep ainlm- 

 lacral furrow. Miller also found minute plates indicating that 

 the abdominal cavity and perhaps also the excavated sulci in the 

 arms were protected by a plated integument. 



It thus appears that the calyx of Poteriocrinus, acccording to 

 Miller, is composed of three rings of plates, 5 underbasals, 5 basals, 

 and 5 radials ; that there are not less than two anal plates, one alter- 

 nating with the basals (intercostals) and another between the ra- 

 dials ; that the radials in the two then known species are excavated 

 for the attachment of the brachials, the articulating scar occup3 7 ing 

 only one-third the width of the plate; that in P. tenuis, the only 

 species in which any part above the calyx was known, there is only 

 a single brachial which is a very long, slender plate, and that the 

 arm joints, so far as known, were found to be long and propor- 

 tioned like the brachials. The calyx of both species is subcorneal, 

 and both came from the Subcarboniferous of England. Miller 

 describes the basals as being hexagonal, which is not quite cor- 

 rect. It was shown by de Koninck and Lehon that three of the 

 subradials (basals) are hexagonal or heptagonal and of a similar 

 form, while the other two those in contact with the anal plates 

 have one or two additional sides, and are slightly larger. The 

 same authors also point out the fact, that four of the radials are 

 of equal size, pentagonal, regularly alternating with the basals, 

 but that the right posterior one, which is rather smaller and 



