146 FOSSIL CRINOIDS. 



designated type, Pachylocrinus subaequalis, described by Hall in 1861 as Scaphio- 

 crinus aequalis (Bost. Journ. Nat. Hist., VH, 316). It is one of the most abun- 

 dant and best known species of the famous Crawfordsville Crinoid beds of the 

 Keokuk Group, and specimens of it are to be seen in almost every museum; and 

 it is a perfectly characteristic example of the type hitherto called Scaphiocrinus. 

 It represents all the essential characters of the group defined by us under that 

 name in Revision, I, 112, including what we called Pachylocrinus; viz, aPoterio- 

 crinus anal side (radianal) ; straight facets occupying the full width of the radials ; 

 and pinnulate arms; — to which may be added, from the assemblage of species 

 listed under it, dichotomous arms, branching more than once; brachials uniserial 

 and usually cuneiform; ventral sac strong and club-shaped. Therefore, having 

 a type species, with definite and well known characters, the status of the genus 

 may be accurately fixed. 



The genus, with its large number of species, is still rather unwieldly, and may 

 probably be subdivided later, perhaps on the form of the cohumi, which is in 

 some species sharply pentagonal, and in many round. Unfortunately the 

 species named as type for the group called Scaphiocrinus, S. dichotomus of Hall, 

 is a very inconspicuous one, which has never been figured, and shows only the 

 most general characters; the only character that can be noted to distinguish 

 it from the Pachylocrinus group is that of Section a, having simple brachials, 

 i. e. only one IBr, as against two or more. It is not my purpose, however, to 

 follow up these finer distinctions; my present interest is to get the names straight- 

 ened out, so that labels in collections may be corrected. 



This leads back to the name of the type species of Pachylocrinus, above men- 

 tioned, about which there is a curious complication, which may as well be taken 

 up now, as some systematist is sure to do sooner or later. Described by Hall as 

 Scaphiocrinus aequalis {loc. cit., 1861), the name was changed by Wachsmuth 

 and Springer (Rev. Pal., I, 116) because of supposed conflict with Poteriocrinus 

 {Scaphiocrinus) aequalis of the same author, described in the Supplement to the 

 Geology of Iowa, 63 (1860). This last species has been listed in the same way — 

 aequalis — hy S. A. Miller (N. A. Geol. and Pal., 273), and Weller (Bull. 153, 

 U. S. Geol. Surv., 540). But the fact is, that the name of Hall's species in the 

 Iowa Supplement (an entirely different one from that of 1861, being a very 

 conspicuous, large form in the Lower Burlington Limestone) is "aqualis," 

 pertaining to water, — a wholly different word from "aequalis," equal. Hence 

 the supposed conflict did not exist, and both of Hall's names will have to stand. 

 So the type of this genus must be written Pachylocrinus aequalis (Hall) ; and the 



