192 PROCEEDINGS OF THE ACADEMY OF [1881. 



second or upper row of interradials, the first interradial, -which 

 exceptionally in this group is placed almost within the dome 

 regions, is identical with the outer interradial plate of Coccocrinus, 

 and as such forms part of the apical and not of the oral system. 



This Adew differs somewhat from that expressed by us in Part 

 I, p. 13, where we stated that the oral plate of the Cyathocrinidse 

 had " no representative in the vault of the Actinocrinidse.atleast not 

 externally ; " we were not at tliat time acquainted, with the genus 

 Coccocrinus^ which has given us new light upon the subject. We 

 have thought heretofore that perhaps the triangular porous 

 structures arranged around the inner test of many Actinocri- 

 nidae, might be the homologues of the oral plates. 



The vault throughout the Sphjeroidocrinidfe is perforated with 

 a single opening, which in all of them is more or less exeentric ; 

 in some lateral and placed toward the periphery of the disk ; in 

 others sub-central leaning toward the posterior side of the body. 

 The construction of the parts at the inner surface of the dome 

 proves that the opening communicated with the posterior side of 

 the visceral cavity, not with the digestive organs. It is sejDarated 

 from the ambulacral and oral systems by a strong partition 

 attached to the inner surface of the vault, and hence the opening 

 represents the anus, and is not the oral aperture, as has been 

 supi^osed by the earlier writers. 



The anus is either in the form of a simple opening through the 

 vault, or is prolonged into a tube, which in Batocrinus sometimes 

 attains a length of three times the height of the body including 

 the arms. The tube is in all cases composed of heavy, generally 

 nodose, wedge-form pieces, which are firmly put together, giving 

 but little flexibility to the structure. It has no openings or pores 

 through its plates or at the sutures, but has in the centre a 

 comparatively small passage, with a minute outlet at the extremit3^ 

 In cases where the anus is not extended into a tube, the aperture 

 is generally situated within the centre of a wart-like inflation com- 

 posed of very small pieces. It is possible that in such cases the 

 small inner plates formed a little pliable tube, which could be 

 drawn in by the animal like the anus in recents Ci'inoids,^ but a 



^ In the genus Codonites of the Blastoidea, we find in connection with 

 the anal opening a similar little tube, which we found in one specimen 

 extended outward, while in another, traces of its little plates are left 

 within the opening. 



