1890.] NATURAL SCIENCES OF PHILADELPHIA. 347 



As another proof that there actually were two integuments in some 

 Ci'ijioids, we considered Siphonocrinus armosus from the Niagara 

 group. This species, so well known from natural casts, apparently 

 has a large trumpet-shaped, subtegminal anal tube, which crosses the 

 mouth, overlies the upper part of the anterior ambulacral tubes, and 

 is continued subtegminal ly all the way to the anterior side of the 

 calyx, even beyond the arm regions, where it bends outward. The 

 case is best illustrated if we imagine the disk of a recent Crinoid, 

 with an anal tube like that of Antedon regalis (Chall. Rep. on 

 Comat., PI. 46, fig. 2), extended out all the way to the arm bases of 

 the anterior ray, and covered by a vault. 



It seemed to us beyond a doubt that in the foregoing cases two 

 distinct structures covered the body, and it was upon these specimens, 

 principally, that we based the opinion that the Camerata had a vault 

 and a subtegminal disk. In taking this view, we did not overlook 

 the fact that in many of these Crinoids, throughout different groups, 

 the covering plates of the ambulacra are exposed upon the surface ; 

 but this seemed to us not to offer any serious objection, for the am- 

 bulacra in all Camerata, at one place or another, come to the surface 

 from beneath the " vault," whether within the limits of the calyx or 

 at the bases of the free arms. A very interesting case was illustrated 

 by us in our Revision of the Palaeocrinoidea, Pt. Ill, PL V, fig. 9; 

 in which the ambulacra do not enter the surface at the outer edges of 

 the orals as in most species of Platycrinus, nor at the arm bases, but 

 at a place midway between orals and arms, from beneath the smaller 

 vault plates. 



It is a striking fact, in the Crinoids as elsewhere, that some char- 

 acteristics which are of the utmost importance from a morphological 

 point of view, prove to be of comparative little value for classifica- 

 tory purposes. This is the case to a very high degree with regard 

 to the ambulacra of the Platycrinidae and Actinocrinidae, which 

 may be tegminal or subtegminal. In the Platycrinidae the covering 

 pieces are generally exposed in the calyx ; in the Actinocrinidae, 

 however, they are, as a rule, hidden from view, or were supposed to 

 be so. But the opposite is also the case in both groups, and even 

 within the limits of a genus. Actinocrinus stellaris from Belgium 

 has large, well-defined covering pieces passing out from the outer 

 edges of the orals ; while most species of Adinocrinas only have in 

 place of them so-called radial dome plates of a first, second and 

 third order, according to the number of bifurcations in the calyx. 



