Vol. 55.] DE. A. W. KOWE ON THE GENUS MICKASTEE. 495 



Though all the accessible literature ou the subject has been studied, 

 the conclusions here set forth have not been influenced by previous 

 publications, for rigid zonal collecting has been the paramount object, 

 Bnd the facts brought out by analysis have been allowed to speak 

 for themselves. The scope of the present paper will not admit of 

 the discussion of questions of nomenclature, which must be left to 

 systematists ; but in order to avoid confusion, a reference will be 

 given, when discussing species, to clear and accessible plates ; and 

 where these are insufficient, illustrations will be fouad in the plates 

 which accompany this text. 



The genus Micraster is of such high palaeontological interest, of 

 such value as a zonal guide, and its literature is so abundant and 

 long established, that it is a matter of no small wonder that any 

 uncertainty should exist concerning the claim of several marked and 

 familiar forms to a specific distinction. 



Few fossils are more common or characteristic in the Chalk of 

 England or the Continent than Micraster^ and yet, though M. eor- 

 anguinum, Leske, was described in 1778, M. cor-testudinarium, 

 Gldf., in 1826, M. Leskei, Desm., in 1837 (the M. breviporus, Ag., 

 1840, of English writers), and M. cor-bovis, Eorbes, in 1850, we 

 fitill seem to have qo authoritative information to guide us in deciding 

 whether these more or less markedly differentiated forms are mere 

 palseontological curiosities, or whether they are culminating points 

 in a scheme of progressive evolution — for, after all, even a marked 

 variety has no claim to special distinction, unless it is fairly abun- 

 dant, and possesses features which stamp it as characteristic of a 

 definite horizon, and place it apart from its fellows. 



On making enquiry of well-known English palaeontologists and 

 field-workers, the writer was struck with the utter lack of 

 unanimity in their opinions — some looking upon these marked 

 forms as mere meaningless varieties, and others regarding them as 

 definite species with a distinct zonal importance. It is rather 

 anomalous that the other common Chalk urchin, Ecliinocorys vulgaris, 

 should, by common consent, have its various and by no means 

 valueless forms reduced to the level of varieties, while Micraster 

 should have its species multiplied to an unnecessary extent. Of 

 the making of species ther^i is no end ; and this, in the case of 

 Micraster, seems to have been especially prevalent on the Continent. 

 On this head, so far back as 1850, d'Orbigny plaintively remarks 

 that there are no less than sixteen species recorded, and he then 

 proposes to reduce them to six. When a species, such as M. trojji- 

 dotus, Ag., is founded on a single example, and that badly damaged, 

 it is reasonable to ask whether it is justifiable to coin new species, 

 in the case of genera which are very common and prone to remark- 

 able variation at each separate horizon, save on the evidence of 

 hundreds of zonally-coUected examples. 



If we could start de novo, and work out the whole series from an 

 evolutional point of view, giving appropriate specific names in the 

 rare instances where they are needed, and marking salient mutations. 



