2 BULLETIlSr 115, UNITED STATES NATIONAL MUSEUM, 



the discrimination of species. This was followed by complete ex- 

 tinction, no vestige of this or allied types having ever been found in 

 later formations. 



The forms in question are all included in the suborder Camerata, 

 but for lack of material the treatment of them in the monograph of 

 that group by Wachsmuth and myself in 1897^ was inadequate. A 

 considerable number of new species has been since described by 

 other authors, and I have in the meantime accumulated much addi- 

 tional material. This in conjunction with the types of the later 

 described species — chiefly in the Walker Museum of the University 

 of Chicago, generously placed at my disjjosal by Doctor Weller — 

 will afford the information necessary for a more satisfactory discus- 

 sion and illustration of these genera. Many drawings for this pur- 

 pose were prepared some years ago, but the further preparation and 

 publication of the memoir have been delayed by the pressure of other 

 work. 



The occasion for the present paper is the desirability of making 

 available for the use of others some of the matter which I have long 

 had in manuscript bearing upon the generic relations of the several 

 forms comprising this group, including the recognition of two new 

 genera. 



The group belongs to the Camerate family Melocrinidae, which was 

 for convenience divided by Wachsmuth and Springer ^ into two sec- 

 tions, Melocrinites and Dolatocrinites, based upon characters not 

 sufficiently constant for family distinction. By transferring the 

 genus Patelliocrinus to the first of these sections and placing it next 

 to Macrostiilocrinus with three basals, we shall have the two sections 

 somewhat better defined with reference to the general habitus and 

 form of calyx than they have been when depending upon the very 

 slight and indecisive difference in the plates of the anal interradius 

 above the first range. The genera of the first section all have a more 

 or less elongate calyx, the dorsal cup being usually higher than wide, 

 subturbinate in form, expanding from a relatively narrow base to 

 the zone of greatest width at the level of the arms. In the second 

 section these characters are more or less reversed, the cup being 

 usually subovoid or hemispheric, broadly rounded, and wider than 

 high. Technocrinus may be regarded as an intermediate form, the 

 earlier species, now herein described, being of the latter type. 



The new genera are proposed for forms, one of which was de- 

 scribed by Miller and Gurley as Stereocrinus indiancnsis, and the 

 other by Lyon as Hadrocrinus plenissimus, and both of which are 



'North American Crinoidea Camerata, Memoirs Museum Comparative Zoology, Harvard, vol. 21, pp. 

 304-329. 

 < North American Crinoidea Cjimerata, pp. 264-267. 



