8 I.ARVIFORM CRICOIDS 



rather than a number of distinct forms, some of which are represented by 

 numerous individuals. 



It is significant that the Indiana specimens occur at a lower horizon 

 than the Illinois and Missouri forms, which are from stratigraphically equiv- 

 alent beds, and are distinct specifically, indicating that these tiny crinoids 

 were short-ranged forms. Although the individuals obtained are compara- 

 tively few in number, they were probably very abundant, as in each case only 

 a small amount of material was examined. The occurrence of these tiny 

 crinoids at widely separated localities and at several horizons, as well as their 

 great diversity of form, suggest that they may prove valuable for strati- 

 graphic correlation, and the micropaleontologist who is concerned with the 

 Pennsylvanian formations may be required to include the Echinodermata in 

 his field of observation. 



FAMILY ALLAGECR1NIDAE 

 In 1881 Carpenter and Etheridge published a description, accompanied 



by two plates of excellent illustrations, of a group of very small and peculiar 

 crinoids collected from the Lower Carboniferous limestone of Scotland, and 

 proposed for them the name Allagecrinus aitstinii [2]. 1 They were unable 

 to assign these forms to any previously recognized family of the Crinoidea 

 and therefore instituted a new family, the Allagecrinidae. This group, which 

 was all included in the single species A. aitstinii, is diverse in character and 

 contains forms which differ from each other in such important respects that 

 they probably represent not only a number of different species but also several 

 generic types. Among the specimens studied by Carpenter and Etheri* 

 are three fairly complete ones which they considered to be adult. These are 

 figured on Plate XV which accompanies their article and the one represented 

 by figures 2a, b, and c, as it is the best preserved, should be considered as the 

 type, and from it rather than from the group as a whole the characters of 

 the genus may be known. 



< >n Plate XVI of Carpenter and Etheridge's article are figured a num- 

 ber of specimens which were considered to be immature individuals belonging 

 to the same species as the "adult" forms. These smaller specimens all possess 

 an oral pyramid which is apparently absent from the "adult" specimens. 

 One individual of somewhat intermediate nature is shown in figures 7a and b 

 on Plate XV — this resembles the "adult" forms in general hut seems to 

 possess, sunken down between the radials, a small oral pyramid. This speci- 

 men is the only connecting link between the "immature" and "adult" forms 

 and had it not been found it would not have occurred to Carpenter and 

 Etheridge to join this whole group into a single species. 



There are several important objections to considering the smaller forms 

 immature examples of the larger ones: (1) all of the "adult"' specimens 

 1 Bracketed numbers refer to bibliography, pp. 5-C. 



