370 PROCEEDINGS OF THE ACADEMY OF [1890- 



and aiftiiu l)y a vault, which is exceedingly improbable. The ani- 

 bulacral skeleton itself is not preserved in the specimen, but the 

 place it occupied is clearly indicated by shallow grooves, which ai'e 

 formed by the thickening of the plates all along the interradial 

 spaces. 



The internal structui'e of Physetocrlnns gives us the key to that 

 of Batocrin.ns, Dorycriiius, Actiiiocrinus, and Teleiocrinus, in all of 

 ■which, Ave are no longer in doubt, there is but one integument, and 

 the part which we had heretofore regarded as the disk constitutes 

 the poriferous portions of the plates. That in these forms the re- 

 spective parts are continuous, connected by small surfaces or pillars, 

 was pointed out by us in the Revisioi> (Pt. II, pp. 26-27, and Pt. 

 Ill, pp. 60 and 61). We gave there a full description of the pores 

 and imbedded passages " evidently for the free circulation of 

 water"; but misunderstood the relations of the ambulacra to sur- 

 rounding parts. We then supposed that the sharp, slightly over- 

 hanging edges of the interradial partitions, along the sides of the 

 ambulacra, were closed beneath them ; which proves not to be the 

 case. The ambulacra in all specimens in which they have been pre- 

 served, are visible from within the calyx. 



The inner structure of these Actinocrinidae always reminded us of 

 the double test in the Clypeasteridae, in which the two parts are con- 

 nected by similar pillars, and we think it highly probable that we have 

 here among these Crinoids a complex vascular water system, which 

 extended all the way up from the interradial plates of the dorsal cup 

 to the upper end of the ventral disk. Such a complex system was not 

 necessary in recent Crinoids in which the whole ventral surface is 

 perforated, and the water could be brought in contact with any part 

 of the body, but the case is different in the Caraerata, in which the 

 tegmen is almost perfectly solid. 



There are good reasons to believe that in the Camerata the water 

 was introduced near the arm bases thi-o ugh small openings, described 

 by us (Revision, Pt. II, p. 51), as respiratory pores, and then fol- 

 lowed the canals and passages along the test. We have observed 

 such openings not only in the Actinocrinidae, but also in the Melo- 

 crinidae, and Rhodocrinidae. In the genus Dolatocrunts they are 

 slit-like as in Oi)hiurids. Like the round openings of Batocrinns 

 and Actinocrimis, they are located between the rays and their main 

 divisions, a little above the arm region. Some species have from 4 

 to 6 of these slits to each interradius, and 2 to 4 to each interdis- 



