John Young — On a Carboniferous Echinoderm. 301 



former for the ortho- and tlie latter for tli'e clino-pinakoid. In the 

 Triclinic system all the axes are slanted, and the symbols would be 

 -written Tzra for the ujoper right posterior and lower left anterior 

 faces of the doubly-oblique rhombic pyramid, 777" h for the upper 

 right anterior and lower left posterior faces, 355^ c for the lower right 

 posterior and upper left anterior, etc.. ; while for the corresponding 

 prism we should have r^T^a f/zh etc. 



The following lists, with the formulse of Naumann placed opposite, 

 will, I think, sufficiently explain all that requires explanation : 



Cubic System. 



Sexagonal System. 



Monoclinic System. 



•nr 



Ttr. P 



•nr P 



-ip' 00 00 



^. ooP+OP 



^ ooP+OP 



■W °oO 



•fifl mPn 



T7T & T1? i? CO +:p CO 



•hr mO 



^1 ooPn+OP 



vr,&2^ QoiPco +CO J?oo +0P 



■hf mOm 



Wr E 





5jf 00 On 



H*€J mEn 



Triclinic System. 



■*t€ mOn 





y?r abed /P/ 



irp - 





i^abcd oo;p;+op 



.. 1 mom 



*nr 2 



ir m 



TTT 2 



11 *■ mOn 

 III., 2 



RJiomhic System. 





vr P 



Tetragonal System. 



ajf. ooP+OP 

 •ffr&v^ P^ + P56 



ire p 



4^ ooP + OP 



t r- 00 n 



rit: 2 



■nr»&-aF 00 P^ +00 PX 



■W- mPn 



M t-^-1 



•nr (fefiT P 00+P^ 



£^ ooPn + OP 



INDEX OF SIGNS. 

 Common bar. 



,, ,, (Hemihedi-al). 



An axis cut normally. 

 „ ,, ,, at m. 



55 55 55 55 '^' 



„ ,, passing uncut to infinity. 

 „ inclined axis passing uncut to infinity. 

 Common bar of Macropinakoid and Macrodome. 



,, ,, Brachypinakoid and Brachydome. 



A clino-diagonal cut. 

 A basal plane. 

 An axis lying at infinity to the particular face described and 



not cut by any plane dissimilar to that face. 

 An axis cut at an abnormal distance and not concerned in 

 the formula. 



VI. — On a Caebonifekous Genus of Echinoderms with 



Overlapping Plates. 



By John Young, 



of the Hunterian Museum, College, Glasgow. 



AFTEE reading the review of Prof.Wyville Thomson's " Depths 

 of the Sea," in the May Number of the Geol. Mag., in which 

 a figure and short description are given of a new living Echinoderm, 

 which Prof. Thomson has named Calveria liystrix, one of whose 



