226 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



"The dimensions of Prof. Sedgwick's specimens are as follows: 

 "Breadth of disk, 8/12ths inch. 

 "Average breadth between arms, 5/12ths inch. Breadth of 



an arm, at its junction with the body, 1/1 2th inch. 

 "Locality and, geological horizon. Silurian, from Ludlow rocks 

 at Docker Park, near Kendal, Westmoreland (specimen figured), 

 associated with Encrinites, and at Benson Knot, also near Kendal, 

 hi hard sandstones, full of characteristic Ludlow fossils." 



Gregory restudied this genus and in 1897 defined it as follows: 



"Protasteridse with a well-marked disk; long, tapering, very flexible 



arms. Some of the adambulacral ossicles are Y-shaped. Scales of 



the disk fairly large. Type species. Protaster sedgwickii, Forbes." 



Gregory remarks that "Forbes's figures of the arm-structures are 



not satisfactory," 



figure 23 as drawn 

 by the former. 

 This illustration 

 a b shows each set of 



FIG. 23. AMBULACHALIA AND ADAMBULACRALIA OF PROTASTEB SEDGWICKII, 

 AFTER GREGORY, a, NEAR THE DISTAL END; 6, IN THE MIDDLE; c, AT ambulacralia dif- 



THE PROXIMAL END. THESE DIFFERENCES ARE DUE TO PRESERVATION. 



tion thought to be due to preservation and adhering rock rather than 

 to structure (see fig. 28, on p. 242). 



Madreporite probably abactinal in position. 



In regard to the term Encrinaster, see Encrinaster (Aspidosoma) , 

 page 242. 

 Protaster has the following species : 



P. sedgwickii Forbes. Ludlow of England. 

 P. biforis Gregory. Wenlock of Wales. 

 P. groomi Sollas and Sollas. Ordovicic of England. 

 ' P. (?) whiteavesianus Parks. Black River. 



P. (t) salteri (Salter). Ordovicic of Wales. 

 . P. (?) stellifer Ringueberg. Rochester. 



PROTASTER BIFORIS Gregory. 



Text figs. 24, 25. 



Protaster biforis GREGORY, Proc. Zool. Soc. London for 1896, 1897, p. 1032, figs. 

 2, 3 on p. 1033. SCHONDORF, Jahrb. nassauisch. Ver. Naturk., Wiesbaden, 

 vol. 63, 1910, p. 238. 



Original description. "Disk fairly large; interbrachial outlines 

 concave. The syngnaths are simple, prominent, and stout. The 

 ambulacral ossicles consist of a thick body and a stout curved wing. 

 The distal margin of the ossicles is notched by a depression for a 

 ventral muscle-field, which also cuts into the proximal margin of the 

 adjoining ossicle. Owing to these muscular depressions the arm has 

 apparently two series of pores. 



