99 



superficial extent of the walls of the folds although altering the form to 

 correspond with the decreasing aperture, the result would be a deeply 

 folded, flask-shaped sack, with a small round orifice like fig. 55a, which is 

 the internal gill of a spider. 



.In Falmcystites tenuiradiatus, a species very characteristic of the 

 Chazy limestone, the whole surface (in the condition in which the fossil is 

 usually found) is covered with deeply striated rhombs, the fissures being 

 deepest where they cross the suture and growing gradually shallower as 

 they approach the centre of the plates, where they die out altogether. 

 Detached plates occur in vast abundance, but no perfect specimens have 

 ever been found. I discovered, however, several fragments of the body 

 sufficient to give the general form and to show that, when the surface in 

 perfect, all these fissures are completely covered over by a very this 

 shell, and that, where they cross the suture there is a small pore in the 

 bottom of each which penetrates to the interior. The rhombs of this 

 species are thus external hydrospires. The fissures seen in the ordinary 

 weathered specimens are the remains of flat tubes like those of Caryo- 

 crinus, situated on the outer instead of the inner surface of the test. The 

 chylaqueous fluid passed outward through the pores and filled the tubes, 

 to be serated through the thin external covering by the surrounding 

 water. In Canjocrinus the water passed inward, through the pores, into 

 the tubes and aerated the fluid within the general cavity of the body. 



The discovery that the fissures and pores of the Cystidea do not 

 communicate directly with the general cavity of the body is entirely due 

 to Mr. Rofe. After reading his highly important paper, I re-examined a 

 great number of specimens and found sufficient to confirm his observa- 

 tions. 



3. On the genus Coclaster. 



Every author who has described a species of this genus has remarked 

 the peculiar striated areas in the interradial spaces. Prof. McCoy, the 

 founder of the genus, pointed out their resemblance to the hydrospires of 

 the Cystidea, but it was Mr. Rofe who first showed that they were also 

 identical in structure therewith. On comparing one of those with that 

 of the cy stidean Pleurocystites, fig. 5i, we at once perceive that they are 

 the same in the external form while Mr. Rofe's figures show that the 

 section 56 d, d, has the structure of fig. 57, which only differs from fig. 54 

 Z), in being straight above instead of concave, and in being divided into 

 two parts. This division is the result of the position of the arm which 

 <5uts the hydrospire in two, in a direction parallel to the fissures- By 



