116 IOWA STUDIES IN NATURAL HISTORY 



genital pores large near outer end of plate; ocular pores very 

 small, about half way between center and distal margin ; genital 

 plates each with a large secondary tubercle, 3-6 large miliaries, 

 and half a dozen or more minute miliaries; oculars with 3-6 

 large, and a number of minute miliaries. Periproct covered with 

 about 20 plates, among which the suranal is scarcely distinguish- 

 able ; the larger plates each carry 1-3 large miliaries. 



Peristome large, about 22 mm. across, wath deep gill-slits ; it is 

 well plated but not heavily so ; buccal plates large, nearly circu- 

 lar, the two of a pair close together, the pairs separated from 

 each other by about a millimeter. Each buccal plate carries 

 about half a dozen slightly club-shaped miliary spines, besides 

 numerous small stout tridentate pedicellariae. Most of the non- 

 ambulacral plates of the peristome carry one or more miliary 

 spines besides small stout tridentate pedicellariae. 



Primary spines about 12 mm. long at ambitus, terete basally 

 and becoming flattened only slightly near tip ; the tip itself is 

 concave, not pointed ; each spine has 20-22 well marked stria- 

 tions. Secondary and miliary spines, slender, cylindrical, bluntly 

 pointed. 



Pedicellariae numerous and diversified but only the small stout 

 tridentate are at all common. In size and form the pedicellariae 

 offer no characters by which they can certainly be distinguished 

 from those of P. maculata. Globiferous pedicellariae rare, of 

 two sizes, one with valves about .80 mm. in length, the other 

 with valves about half as large. Ophicephalous pedicellariae 

 rare, with valves about .50 mm. long and loops .15 mm. more. 

 Tridentate pedicellariae in at least three forms: (a) slender, 

 with valves, 1.25 mm. long; (b) small stout, with valves about 

 .50 mm. long; and (c) big, stout, with valves over a millimeter 

 long, half a millimeter wide and verj- serrate margins; only one 

 of these big pedicellariae was noted. Triphyllous pedicellariae 

 with valves .22 mm. long and about .18 mm. wide near tip. 



Color (in alcohol) pale brown wath a distinctly greenish cast, 

 the midzone with about 20 large irregular blotches of a dis- 

 tinctly darker shade; there are two of these blotches in each 

 ambulacrum and interambulacrum but they vary in size and 

 distinctness. Primary spines pale fawn-color, decidedly greenish 

 basally and very faintly pinkish at tips; on the dark blotches 



