206 Proceedings of the Royal Irish Academy. 



XXXI. Ox A MAXFOPtilED COEONA OF ECHINTS ESCTTLEKTrS. Ey 



H. W. MACEDfiosH, E. A. (Vith Plates 21 and 22). 



[Read May 10, 1875.] 



The remarkaUe specimen -whiclL is described in the present communi- 

 cation has lain for many years in the iMuseum of the Dublin Univer- 

 sity, having been, as I am informed by Professor Dr. Perceval Wright, 

 dredged up by the late Dr. Ball off the coast of Toughal. 



I had often noticed it in the coni"se of my museum studies, on ac- 

 count of the prominent pouch which the actinal (oral) aspect presents, 

 but had not bestoTved more than a casual iaspection on it till recently, 

 when its many peculiarities so forced themselves on my attention, that 

 I requested and obtained peiinission of Professor Dr. Macalister, 

 the present Director of the lluseum, to place a short description of 

 it on record. 



In describing the present specimen I shall not attempt anything 

 like a detailed notice of all its peculiarities. Such a proceeding 

 would be but of little value or interest, and a mere abstract descrip- 

 tion of such a shell would convey but little idea to the mind ; hence 

 I prefer relying on the di'awings'^" for this purpose, and will only indi- 

 cate here the chief features of interest. 



Por purposes of convenience the madreporic plate — placed pos- 

 teriorly — and corresponding interambulacnim will be numbered I, the 

 next genital plate on the left, and its interam- 

 bulacrum will be II, and so on from left to 

 right ; the ocular plate and ambulacrtim on the 

 immediate left of the macbeporic, will be 1, the 

 next on its left 2, and so on in the same order; 

 and, since each area has a double series of plates, 

 these will be called I a, 1 1, &c., or 1 a, 1 1, (Src, 

 respectively. I adopt this method simply for 

 convenience and not with any reference to the 

 views put forward by Professors A. Agassiz or 

 Loven, as to the position of the macbeporic plate. 



Looked at as a whole, the corona is seen to be considerably flat- 

 tened on the madreporic side, which is produced on the actinal surface 

 into a sort of boss or pouch (Plate 21, fig. 2). The mouth is eccentric, 

 displaced to the lower left-hand side ; the auricles are normal. In the 

 abactinal system, plate I (madi'eporic), is unsymmetiical, beiag pro- 

 longed at the upper left-hand comer, and has but little of the character- 



* WTiieli have been all taken under the camera lucida. As the outlines of 

 the plates are the most striking part of the corona, I have drawn them as accurately 

 as I could and have therefore laid down the tubercles almost orthographically. 



