NATURAL SCIENCES OF PHILADELPHIA. 143 



sometimes also the second arm pieces a little longer than wide, and slightly 

 constricted ; other arm pieces generally wider than long and wedge shaped, 

 but not arranged so as to impart a zigzag appearance to the arms. Oolumn 

 small, nearly or quite round, and composed near the base of alternately thin 

 and thick pieces. 



Height of body to top of first radial pieces, 0-07 inch; breadth, 0-20 inch; 

 length of arms, about 0-70 inch. 



This little species seems to be nearest like S. dichotomus, Hall (Iowa Report, 

 p. 553), with which it agrees in size and general appearance. It will be read- 

 ily distinguished, however, by the more frequent bifurcations of its arms, 

 which also differ in being more rounded and composed of proportionally longer 

 pieces, not arranged so as to present a slightly zigzag appearance, as in the 

 species dichotomus. It will also be distinguished from the last by having two 

 arms to each ray all around, as well as by its concave base. 



Locality and position. Upper division of the Burlington group, at Burlington, 

 Iowa. Lower Carboniferous. No. 286 of Mr. Wachsmuth's collection. 



ScAPHiocRiNUS Tethys, M. and W. 



Body under medium size, expanding rather rapidly from the column to the 

 top of the first radialFs, where it is about one-fourth wider than high. Base 

 small, twice to three times as wide as high. Basal pieces very small, wider 

 than high, and pentagonal in form. Subradial pieces slightly wider than long, 

 pentagonal, excepting two on the anal side, which are hexagonal, there being 

 no well defined angle at the middle of the base of any of them. First radials 

 larger than the subradials, a little wider than long, and all pentagonal. Sec- 

 ond radial pieces rather more than twice as wide as long, rounded and a little 

 constricted in the middle, and somewhat expanded at the ends ; all pentagonal 

 in outline, and each supporting two arms on its superior sloping sides. 



Anal series consisting of two alternating vertical ranges of pieces, the first of 

 which rests between the two upper sloping sides of two of the subradials, and 

 supports an inferior sloping side of the first radial on the right, while its left 

 side above the middle connects with another anal resting upon the truncated 

 upper side of one of the subradials, and connecting with the first radial on the 

 right. Above these one or two ranges of similar pieces join with those form- 

 ing the base of the so-called proboscis. 



Arms not positively known to bifurcate after their origin on the second radial 

 pieces ; composed of joints, the lower of which are twice to three times as long 

 as wide, and rounded or subangular, and narrower in the middle than at the 

 ends. Above these the pieces gradually become shorter, and more distinctly 

 expanded at the ends, with the upper lateral extremity of each somewhat pro- 

 jecting alternately on opposite sides, so as to present a distinct zigzag arrange- 

 ment, the projection being for the support of the pinnulas, which are compara- 

 tively rather stout, and composed of joints two or three times as long as wide, 

 and provided with deep ambulacra] furrows within. 



Column comparatively rather stout; subpeutagonal near the base, but soon 

 tapering and becoming rounded below; composed below of uniform pieces ; 

 about one-third as thick as wide, but gradually becoming thinner near the base 

 of the body. 



Length of body to top of first radial pieces, 0-17 inch; breadth about 0-22 inch; 

 length of arms, about 1-10 inch. 



This species is related to that we have here described under the name S. na- 

 nus, but not only differs in having longer arms, but in having its second radial 

 pieces and all of its arm joints much longer in proportion, as well as present- 

 ing a more strongly zigzag arrangement. Its base is also more protuberant, 

 and the sutures between its body plates slightly impressed instead of even. 



Locality and position. Upper division Burlington group, at Burlington, Iowa. 

 Lower Carboniferous. No. 298 of Mr. Wachsmuth's collection. 



1869.] 



