228 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Ventral Structure of Taxocrinus and Haplocrinus.* — Messrs. C. 

 Wachsmuth and F. Springer bave made certain discoveries in the ventral 

 structure of Taxocrinus and Haplocrinus which lead to modifications in 

 the classification of the Crinoidea. They have found that the whole 

 ventral surface of Haplocrinus is covered by five large plates which meet 

 in the centre as in Allagecrinus, and that the " central plate " is a myth ; 

 what had been taken for it was a more or less tongue-like prolongation 

 of the posterior plate, and a fracture in their original specimen had been 

 taken for a suture on the posterior side. They give reasons for now 

 thinking that the apparently central plate of many Platycrinidse and 

 Actinocrinidte is the posterior oral, pushed inward to a central position by 

 anal structures. It would then appear that the five orals of Neocrinoids 

 were represented in the Palseocrinoids by the central plate and four 

 large proxima]s ; and this view does much to reconcile the conflicting 

 views of our authors and of Dr. H. Carpenter ; " the orals being found 

 at last to consist of a portion of the proximals which he has claimed, 

 with the addition of the central plate which we have contended for. 

 This rational result, as often happens in such cases, adopts what was 

 sound, and rejects the errors in the views of both parties." 



A well-preserved specimen of Taxocrinus intermedius has demon- 

 strated that it had an external mouth, surrounded by five parted oral 

 plates, with the ambulacra converging to it and passing in between the 

 orals. The authors have now very little doubt that the structure here 

 discovered is substantially that of the Ichthyocrinidse in general, and 

 that the ventral side of the calyx in this family is morphologically in 

 the condition of Thaumafocrinus, and similar to that of Hyocrinus and 

 Mhizocrinus. After discussing this matter in some detail and considering 

 the alleged points of difference between the Palseocrinoidea and Neo- 

 crinoidea^ Messrs. Wachsmuth and Sjjringer come to the conclusion that 

 this division is not natural. They now think that four well-defined 

 groups can be distinguished as independent primary divisions of the 

 Crinoidea : — 1. Camarata ; 2. Inadunata ; 3. Articulata, including the 

 Ichthyocrinidae ; and 4. Canaliculata ; the last includes most of the 

 mesozoic and recent Crinoids. They are inclined to put Holopus, 

 Bathycrinus, and Hyocrinus under the group Larviforma of the Inadunata, 

 for they are all monocyclic, and retain throughout life large oral plates. 

 Thaumatocrinus may be referred to the Articulata. With these altera- 

 tions the Canaliculata would form a well-defined group, containing only 

 dicyclic Crinoids, in which the underbasals are anchylosed to the top- 

 stem-joint, with which they form the centrodorsal. A revised diagnosis 

 of the IcthyocrinidsB is given. 



Crotalocrinus.t — Messrs. C. Wachsmuth and F. Springer give a 

 detailed account of the structure of this remarkable palaeozoic Crinoid. 

 Its net-formed radial appendages, resembling rather the fronds of a 

 Bryozoan than the arms of a Crinoid, have long made it a puzzle to 

 naturalists. It is only lately that they have had the opportunity of 

 observing actual specimens, and they find that the views as to its struc- 

 ture and relationships which they published in their revision of the 

 Palaeocrinoids were completely erroneous. They now come to the con- 

 clusion that a family of the suborder to be called Crotalocrinidte must be 



* Proc. Acad. Nat. Sci. PhilacL, 1888, pp. 337-63 (1 pi.), 

 t Ibid., pp. 364-90 (2 pis.). 



