120 BULLETIN" 88, UNITED STATES NATIONAL MUSEUM. 



P. wykoffi also greatly resembles Anorfhaster miamiensis, but the 

 interbrachial areas in the latter are entirely composed of adambu- 

 lacral plates, there being no interbrachial marginals present. While 

 both species attained a similar size, another -difference is that the 

 former has a greater number of plates in the adambulacral and 

 inframarginal columns. 



PROMOPAL^EASTER DYERI (Meek). 



Plate 18, fig. 8; plate 20, figs. 3-6; plate 25, fig. 1. 



Palseaster dyeri MEEK, Amer. Journ. Sci., ser. 3, vol. 3, 1872, p. 257; Geol. Surv. 

 Ohio, Pal., vol. 1, 1873, p. 58, pi. 4, figs. 2a-2/. 



Original description (1873). "Among the specimens loaned to me 

 for study and description by Mr. Dyer, there is a very imperfect 

 example of one of the largest known species of Silurian Starfishes. 

 When entire, it could scarcely have measured less than 5 inches in 

 diameter [R = probably 3 inches, or 75 mm.] across from end to end 

 of the rays on opposite sides; and it presents a breadth of disk (as 

 flattened by pressure) of about 2 inches [r = probably seven-eighths 

 inch, or 22 mm.]. Its state of preservation is, unfortunately, such as 

 not to admit of systematic description, but I think enough of its 

 character can be given to enable the student to identify it, by the 

 additional aid of figures. 



"The dorsal side of both disk and rays is composed of numerous 

 small pieces [with stellate extensions], with the pores between them 

 apparently so large that these pieces only seem to touch at three to 

 four salient points of each, so as to form a kind of reticulated struc- 

 ture; while they each bear a little central tubercle, with a minute pit in 

 its top for the articulation of small, short [blunt] spines, generally 

 about 0.07 to 0.09 inch in length, and about 0.02 to 0.03 inch in 

 thickness. [Each plate bears but one of these spines and there appear 

 to be no other smaller spines.] 



"In one of the axilla between two of the rays the so-called madri- 

 poriform body can be seen near the margin of the disk. It is nearly 

 flat, of an obtusely subtrilobate form [probably cruciform], with a 

 breadth or transverse diameter of 0.30 inch, and a diameter at right 

 angles to the same of 0.24 inch [not less than 10 mm.]. Its lobed 

 edge is directed inward toward the middle of the disk, and its middle 

 lobe is largest, and shows the little divisions between the slits or 

 furrows, diverging and bifurcating inward like the nervation in the 

 pinnules of some kind of ferns; while in the smaller lateral lobes these 

 markings diverge outward. 



"The ventral side is also much obscured by the adhering matrix, 

 and numerous detached and confusedly mingled spines. A row of 

 comparatively small, tumid, nearly square [infra] marginal pieces, 



