22 BULLETIN 115, UNITED STATES NATIONAL MUSEUM. 



Miller and Gurley utilized, however, by making new species for all 

 of them), whereas in many other Batocrinoid genera the number is 

 generally constant for the species. Among the Onondaga species of 

 Dolatocrinus the number of arms appears to be usually constant and 

 well correlated with other characters. In the Hamilton the genus 

 reached its acme of development, resulting in an enormous increase 

 in number and variety, followed, as usual in such cases, by extinction. 

 It was a period of active mutation. Several extremely well-marked 

 types were produced, which may readily be distinguished from the 

 Onondaga forms and from one another. Some of these, which no 

 experienced paleontologist would fail to recognize at a glance, include 

 variations in number and grouping of arms and in minor details of 

 surface ornament which, if regarded as essential, would result in 

 making a new species for almost every well-preserved specimen that 

 turns up. In fact, that is what actually occurred as to a large part 

 of Miller and Gurley 's Hamilton species; for in the Gurley collection, 

 containing all the material used in their study of this genus, 18 of 

 their species are represented only by the single type specimen, there 

 being no duplicates except in the other 19. And to show how the 

 use of the arm character would work out in practice, there are in my 

 own collection upward of 20 specimens belonging to the most pro- 

 lific Hamilton form of the locality which have arm formulas different 

 from that of an}^ of Miller and Gurley's species, and every one of 

 them, under their rule, would have to be made the tj^pe of a new 

 species. 



The recognition of the several well-defined and definable Hamilton 

 types will result in the reduction of the species to a reasonable 

 number, within the bounds of probability. I shall attempt to point 

 them out, and to give the names which by reason of priority should 

 be attached to them. Much of the matter contained in the lengthy 

 descriptions (often tedious repetitions of generic characters) is of no 

 practical service for the discrimination of the species. For any 

 valid species it ought to be possible to point out some one definite 

 character, or combination of characters, not due to individual vari- 

 ation or sporadic occurrence, by which it is distinguished and con- 

 trasted with others. Supposed species for which this can not be 

 done should be merged in the nearest one that is well defined. 



The characters which have been chiefly considered in the differen- 

 tiation of species in this genus are the following: 



Form. — The general form and proportions of the calyx are useful 

 characters which mark several well-defined types. It may be rather 

 high cup-shaped, with vertical sides and flat base: bowl-shaped or 

 hemispheric, expanding by a regular curve from a narrow base to the 

 arms; basin-shaped, with nearly straight sides, spreading at a wide 

 angle from a truncate and concave base; depressed bursiform, con- 

 stricted below tlie arm bases, the sides (airving inward to a broad 



