DESCRIPTION OF LEPIDE8THES WORTHENI. 207 



of the ambulacral plates instead of being in the outer portion of the plates 

 as in most Paleozoic Echini. 



Two genera are included at present in this family, Lepidesthes, which 

 is the least specialized in the peculiar line of variation of the family, and 

 therefore is to be considered the most primitive. Uyboechinus was de- 

 scribed as a separate genus by Worthen and Miller (42), but from meager 

 and somewhat doubtful material. The single known species, H. specta- 

 bilis, is included in the genus Lepidesthes by Keyes in his Synopsis (24), 

 and under the circumstances we^ would prefer to leave it there. The 

 type of Uyboechinus spectabilis is in the Illinois State Museum at Spring- 

 iield, Illinois.* The second certain genus of this famil}'' is Fholidocidaris 

 which is the more aberrant genus on account of the irregularity of its 

 ambulacral and interambulacral plates. 



/' 



DESCRIPTION OF LEPIDESTHES WORTHENI, SP. NOV. ^ 



Plate 9, figure 53. 



This species, which is named for Professor A. H. Worthen in consid- 

 eration of his work on American Paleozoic Echini, is represented by a 

 single specimen in the Boston Society of Natural History, catalogue 

 number 11601, and I am indebted to the kind interest of Miss I. L. John- 

 son, who called my attention to it. The specimen has the original cal- 

 careous plates, and as known from associated fossils (Platycrinus hemi- 

 sphericus, M. and W. and Scaphiocrinus depressus, M. and W.) is from the 

 Keokuk group of the Subcarboniferous. The locality is not known, but 

 the fossils were in a blue or grayish and gritty clay, which corresponds 

 with the fine and occasional coarser matrix of material from Crawfords- 

 ville, Indiana. The specimen is probably from this or a neighboring 

 locality. 



The specimen, plate 9, figure 53, is flattened by crushing. On the op- 

 posite side from that figured dental pj^ramids are shown at the oral end, 

 and these serve to orient the axes. The height is 8.6 centimeters ; width, 

 2.7 centimeters. The ambulacra at the ambitus measure 0.9 of a centi- 

 meter in width; the interambulacra measure from 0.5 to 0.6 of a centi- 

 meter in width. The clearest ambulacral area, B, is shown in the figure, 

 plate 9, figure 53. There are seven to eight columns of ambulacral 

 plates. Eight may be counted at the ambitus in one horizontal plane. 

 The plates are subhexagonal in outline, or near the dorsal area, nearly or 

 quite tetragonal. They are very regular in form and arrangement, and 

 each plate is perforated by two pores situated in the middle of the plate. 

 At the ventral border of the ambulacrum only four columns of plates 

 exist, as shown by the figure in area B. These plates differ from those in 



*As I am informed by Mr Wm. F. E. Gurley, ytate geologist of Illinois. 



