On a new Species o/Nucleolites. 125 



XII. — Description of a new Species of Nucleolites, with 

 Remarks on the Subdivisions of the Genus. By Prof. F. 

 Jeffeey Bell, M.A., Sec. E.M.S. 



The Tiaistees of the British Museum have lately acquired by- 

 purchase a small specimen of a species clearly allied to the 

 form which those who use Mr. Alex. Agassiz's ' Revision of 

 the Echini ' would call Nucleolites epigonus. Mart. ; the first 

 point of interest in this acquisition was the locality from 

 which it was derived, for it came, not, like N. epigonus^ from 

 the eastern seas, but from Nassau in the Bahamas. 



But this chorological interest soon paled before the mor- 

 phological ; in N. epigonusj it will be remembered, the anal 

 region looks backwards, is elliptical in form, with the long 

 axis vertical, and the periproctal groove is continued to the 

 ventral surface ; an essentially similar disposition of the anal 

 region is found in Echinohrissus recens. But in the new 

 species we have quite a different arrangemciit ; though the 

 anal region is elliptical in form, the long axis lies trans- 

 versely, and there is no groove reaching to the ventral sur- 

 face ; in these two particulars it resembles Rhynchopygus. 

 Echinohrissus, on the other hand, resembles the new form in 

 having the actinostome wider than long, whereas in N. epi- 

 gonus that orifice is longer than wide. 



In other characters — the arrangement of the ambulacra 

 and ambulacral pores, the general ornamentation of the test, 

 the delicacy and whiteness of the whole test — N. occidentalism 

 as the new species may be called, and N. epigonus agree 

 exactly. 



The question first raised by an annectent form such as this 

 may nearly always be stated in the following terms : — Have 

 the generic divisions which have been made been natural ^ 

 In other words, Have the characters on which genera are 

 based the constancy which makes them of value ? That 

 systematists have attached importance to the form and rela- 

 tions of the oral and anal areas is indisputable. 



In the latest authoritative work on Echinoids generally — 

 I mean, of course, the chapters on Echinoderms in Zittel's 

 * Palseontologie ' — Nucleolites is kept separate from Echino- 

 hrissus, and is thus defined: — " Wie vorige [Echinohrissus'], 

 aber Poren nicht gejocht ; " but if Prof. Zittel was unable 

 to examine an example of E. recens, he should have made use 



