118 CATALOGUE OF THE BLASTOIDEA. 



one small one, the latter being always in the left anterior interradius (A-B). Five 

 radials, more or less deeply incised by the ambulacra, and five interradials which rest 

 on them and bound the peristome, one of them being pierced by the anus. 



Ambulacra fringed on each side by a single or double row of jointed appendages, 

 which are in close relation with the side plates. These rest on or against a subam- 

 bulacral lancet-plate, which is pierced by a canal that lodged the water-vessel and 

 unites with its fellows into a circumoral ring. 



Hydrospires arranged in ten (or rarely eight) groups which are limited to the 

 radial and interradial plates ; their slits are parallel to, and more or less completely 

 concealed by, the ambulacra, often opening externally through pores at their sides, 

 and also by five or ten openings round the peristome. Neither hydrospires nor 

 ambulacra extend below the basiradial suture. 



Peristome naturally concealed by a vault of small plates, which rarely exhibit any 

 definite arrangement, and are continuous with the covering plates of the ambulacra. 



Remarks. — Of the various characters mentioned in the preceding definition some are 

 important because they occur in no other Pelmatozoa, while others, though absolutely 

 constant among the Blastoids, seem to present themselves exceptionally in both Crinoids 

 and Cystids. Others again depend not so much on the presence of particular structures, 

 as on their mode of distribution in the organization of a Blastoid. To the first class 

 belong the perforation of the lancet-plate, of which we have as yet no knowledge 

 whatever in either Crinoids or Cystids. In the second class come the absence of 

 under-basals, the constant presence of five interradials (one of which is divided in 

 Elceacrinus), and likewise perhaps the constant but peculiar trimerous symmetry of 

 the base, which seems to occur also in the rare Cystic! Cryptocrinus cerasus, but in no 

 Crinoid at all with the possible exception of Steplianocrinus. Many Palasocrinoids 

 have a trimerous base, but according to Wachsmuth and Springer 1 the small plate is 

 always in the right anterior interradius (A-E). 



Chief among the third class of characters of the Blastoidea is the very symmetrical 

 grouping of the hydrospires. These organs occur in most Cystids and perhaps even 



1 ' Eevision of the Paloeocrinoidea,' Part III. 1SS5, p. 10. The words left and right are used by the American 

 authors in a different sense from that in which we have employed them, as explained above on pp. 13, 14; 

 and we cannot help thinking that in their description of the azygos basal of Pakeocrinoidea as being located 

 between the anterior and left posterolateral ray, the word anterolateral would have been more correct than 

 j,nsi, rolateral. Since the preceding pages were printed Mr. Wachsmuth has kindly sent us an advance sheet 

 of the forthcoming concluding portion of the ' Revision of the Palseocrinoidea ' by himself and Mr. Springer. 

 In this work, evidence is adduced, which in our opinion is conclusive, to show that Stephanoorinus is no 

 Blastoid at all, but a Brachiate Crinoid. In the few specimens in which we have been able to make out 

 the position of the small basal of S. angulaius (including two which were sent to us by Mr. Wachsmuth 

 himself) it occupies the same position as in the Blastoids, viz. the interradius A-B, as shown in our diagram 

 on p. 17. The American authors state, however, that the small basal of Stephanocrinui is directed towards 

 the azygos side, which is the interradius C-D of our nomenclature ; and as they have examined a large 

 series of specimens both of #. angulatus and of S. gemmiformii, this is probably true. 



