SALENIA VARISPINA. 17 



taken of the homologies of tin- apical system of Echini ami of the plates of 

 the embryonic Comatula in its Pentacrinus stage. Neuinayr's suggestion 

 of the morphological value of the anal plates of the Palaechinidae and Cida- 

 ridaa has thrown considerable light on this question, and shows us the possi- 

 bility of a uumber of anal plates in Echini, say five for instance in Echino- 

 cidaris. being tin- homologue of the dorso-central plate of the Pentacrinus 

 stage of Comatula. Of course we should remember that, in making this 

 homology, we are comparing plates, which while they occupy the same 

 structural position, have a very different physiological value. As I have 

 already staled, we have the most positive proof of the origin of the dorso- 

 central plate of Starfishes and Ophiurans as a single Y-shaped roil appearing 

 simultaneously with the five hasals ; hut we have no Midi definite data either 



lor the Echini or for tin- Comatula- while within the Pluteus. Such informa- 

 tion would go far towards settling this disputed homology, for at present we 

 an- obliged lo draw our conclusions from a comparison of the more advanced 

 stages of development. The discovery of a pedunculated Starfish by the 

 " Travailleur," the Cadaster of Perrier,* may throw important light on the 

 homology of the centro-dorsal plate of the Starfishes and of the Crinoids. 



Tin- discovery by Laube in the Trias of the genus Tiarechinus ofNeumayr 

 shows that the pyramidal anal covering, composed of a few large plates, 

 which appears in some of the earliest Crinoids known, has persisted or re- 

 appeared after a long lapse of time, during which the greater part of the 

 Palaechini were provided with an anal system protected \>y one or two con- 

 centric rings of numerous plates; this last structural feature characterizing 

 nearly all the modern Echini, only a few Clypeastroids and Spatangoids, and 

 among tin- Desmosticha the Echinocidaridae, still retaining tin- antique struc- 

 ture of the anal system, while in nearly all Echini from the oldest to those of 

 the present day we may imagine the numerous anal plates to have been the 

 result of the splitting up of the live lor more ?) plates of the anal p\ ramids 

 into numerous smaller plates. Where this splitting up took place regularly, 



we have the anal aystem of the I'ahechinida-. Cidaridm. etc.; where, on 



the contrary, <>ne plate resisted, we have what exists in Salenia and all the 

 recent Echini, in which one of the anal plates has a great prominence over 

 the others. Tin- Salenia-like structure, therefore, may appear at anytime. 



and disappear again, without perhaps having so important a morphological 



value as I was at first inclined to give it when I called attention to the 



