226 Prof. P. M. Duncan and Mr. W. P. Sladen on the 



nately the specimens of Hemtaster elongatus, nobis, are still 

 in our liands, and we have again gone very carefully over 

 them. It is only just to ourselves to state that in describing the 

 species the more or less exact resemblance of the apical system 

 to that of Palceostoma was not lost sight of; but the construc- 

 tion of the whole actinal area differed so decidedly from that 

 of the genus just named, that we could not entertain the 

 possibility of our form belonging to it. 



Moreover, since the publication of the ' Echinoidea of the 

 Kanikot Group,' we have completed and published a descrip- 

 tion of the fossil Echinoidea of the true Nummulitic rocks of 

 the Khirthar strata of the same region, and amongst them are 

 some forms of another Hemiaster {R. digonus, d'Archiac) 

 with two large generative pores only, and which should 

 equally be the subject of Prof. Loven's criticism. 



The first passage in which Prof. Lovdn refers to our species 

 is on page 73, in a footnote : — " Another stranger is Hemi- 

 aster elongatus of Indian Tertiaries. It is a Palwostoma.^'' 

 The second notice is on page 79, in a footnote : — " A fossil 

 species of this genus from the Nummulitic strata of Western 

 bind has been described as Hemiaster elongatus by Duncan 

 and Sladen, Mem. Geol. Survey India, Tert. Ser. xiv. vol. iii. 

 p. 78, pi. xix. figs. 7-15, 1882." 



We propose in this communication to reply to Prof. Lovdn's 

 statements by arranging our answer as systematically as 

 possible : — 



I. The classification of the Leskiada?, Gray, and the details 

 of those parts of the structures of Pahwstoma which have a 

 special bearing upon its generic diagnosis, with a notice of 

 the descriptions of Gray, A. Agassiz, and Loven. 



II. A notice of Loven's comparison of the genera Palceo- 

 stoma and PaUeotrofus^ and of its bearing upon the method 

 of distinguishing oilier genera. 



III. A description of Hemiaster elongatus^ nobis, so far as 

 the structures bear upon its generic position. 



IV. A description of Hemiaster digonusj d'Archiac. 



V. A comparison of the essential structures of Palceostoma 

 mirabile, Hemiaster elongatus^ and H. digonus. 



VI. A brief notice of the reasons why we still place the 

 two species from Sind in the genus Hemiaster. 



I. 



In the ' Eevision of the Echini,' by A. Agassiz, p. 582, the 

 subfamily of the Leskiada? of Gray is introduced, in order to 



