104 DESCEIPTIOX OF THE HAED PARTS OF SOME 



The abactinal membrane of the disk of Brisinga is eminently Asterian ; 

 it is only sHghtly strengthened by a few minute limestone plates, as is 

 the case in Crossaster and Pycnopodia, and in spite of the general re- 

 semblance, at first glance, of this well-defined disk to an Ophiuran disk, 

 we have nothing whatever corresponding to the arrangement of the cen- 

 tral i^lates so characteristic of the disk of Ophiurans. But we have in 

 a great many genera of Starfishes the central part of the disk, show- 

 ing in the young stages only, as regular an arrangement of the plates 

 of the abactinal system as in any Ophiuran, though it is lost in the 

 adult. Such a young stage is figured in PI. VIII., a corresponding stage 

 has also been recently figured by Loven in his Memoir on the Echini 

 (1875), and a similar structure of the disk will undoubtedly be found to 

 exist in the very youngest stages of each genus, as it seems to be a 

 general structure of the young of all Starfishes, as far as observed. 



While Brisinga is a most important form, as showing the relationship 

 between Starfishes and Ophiurans, there certainly is nothing in its struc- 

 ture or in its affinity to Pro taster to warrant the paloeontological importance 

 ascribed to it by the younger Sars ; and it cannot be considered, any more 

 than several other genera of Starfishes now living,* as the representative 

 at the preseiit day of the oldest-known Echinoderm. I think we can 

 show from the study of the hard parts of Starfishes that they have been 

 a remarkably persistent tj^pe, and that the apparent changes of form 

 due to the excessive increase or diminution of the interbrachial lime- 

 stone deposit is a very secondary feature, which, though greatly modi- 

 fying the external appearance of the Starfishes, yet does not affect the 

 main structure, which, as has been stated, is remarkably uniform through- 

 out the order. "While fully admitting the many important points (so 

 well brought out by Sars in his Memoir on Brisinga) wherein the genus 

 differs from the other Starfishes, yet I must call his attention to the 

 fact that many of the structural details which he strongly insists upon 

 as specially characteristic of Brisinga t are common to the other Starfishes, 

 and do not constitute features by which this family can be contrasted 

 with the remaining Starfishes. 



* Pycnopodia, Crossaster. 



f For an opportunity of examining both dry and alcoliolic specimens of Brisinga, I must thank Sir 

 C. Wyville Thomson, and Dr. G. O. Sars. Brisinga endecacnemos is found in deep water off the Lofoten 

 Islands, Norway. It has been collected by the " Challenger " in eighty fathoms, on the La Have Bank off 

 Kova Scotia. 



