On the Genera of Recent Clypeastroids. 503 



Tills fine mole-rat, ■which I have named in honour of its 

 discoverer, is no doubt nearly allied to G. ochraceo-cinereus, 

 Heugl., with which it shares its chief cranial characteristics. 

 But its colour is of the shrty grey found in G. lechet, and 

 quite unlike the sandy or ochraceous of Heuglin's species. 



LXIX. — The Genera of Recent Clypeastroids. By Hubert 

 Lyman Clark^ Museum of Comparative Zoology, Cam- 

 bridge, U.S.A. 



Although the classification of the sea-urchins commonly 

 called cake-urchins, sand-dollars, and keyhole-urchins has 

 engaged the attention of many zoologists, some of whom 

 have held very high rank, the nomenclature in use at the 

 present day is very unsatisfactory. That which is used by 

 palaeontologists differs from that of their brethren who 

 confine their work to Recent forms, and such a name as 

 Echinanthus, for example, means something quite different 

 in one field from what it does in the other. The difficulties 

 seem to arise chiefly from»the fact that leading echiuologists, 

 such as the two Agassizs, Duncan, and Lambert, have re- 

 fused to accei)t the tenth edition of the ' Systema Naturse ' 

 as the starting-point in nomenclature, but have dated both 

 genera and species from pre-Linnean writers. Other articles 

 of our present International Code of Nomenclature have also 

 been consciously or unconsciously violated, and thus the 

 confusion has been made worse. 



Having had occasion recently to outline for my own use a 

 consistent and satisfactory classification of the Recent Clype- 

 astroida, I have found that tiie application of the Inter- 

 national Code results in some important changes ; and as I 

 believe these changes are bound to be made ultimately, they 

 had better be suggested at once. Fortunately few familiar 

 names are altered, and none of these is likely to cause any 

 confusion. Of course, those who persist in the maintenance 

 of pre-Linnean names cannot accept my conclusions, and I 

 shall not expect it ; but I do hope that those who wish to 

 obtain a reasonable stability of nomenclature through the 

 general acceptance of the International Code Avill find them- 

 selves able to accept the types here given for the different 

 genera, even if their own methods or preferences would 

 have led them to diff'erent results. I hope it is needless 

 to add that if I err in the application of the code or in the 



