138 PROCEEDINGS OF THE ACADEMY OF 



larger than the smaller subradials, longer than wide, and irregularly sub- 

 hexagonal or heptagonal ; facet for the reception of the second radials small, 

 not protuberant outwards, shallow and about one-third as wide as the plates. 

 Arms above the first radial pieces very slender, cylindrical, and composed of 

 a single series of segments from twice to three or four times as long as wide. 

 In some of the rays the first division takes place on the second, in others on 

 the third, and in the anterior ray on the fourth piece above the first radials, 

 after which they bifurcate irregularly once, twice, or oftener, on the second, 

 third or fourth piece. The first anal plate is rather large, and rests upon the 

 upper truncated side of the largest subradial plate, so as to project considera- 

 bly above the first radials. Its left side curves inwards, and its right con- 

 nects with another plate of nearly its own size resting upon a sloping side of 

 the first radial on the right. Above these are seen several other plates, which 

 form together a kind of slender lateral trunk, or proboscis, rising like an arm 

 on a range with the true arms. Some little distance above, it curves in with 

 its upper extremity between the arms, leaving at its base, on the left, a cavity 

 or opening, passing apparently into the body between it and the first arm on 

 that side. 



The surface is finely granulose, and the sutures indistinct. The column is 

 small, round, and composed of nearly equal, rather short joints, near the 

 base. 



A very marked feature of this species, is its peculiarity of having apparently 

 a slender proboscis much like an arm, rising from the anal side, with an 

 opening between its left side and one of the arms. This is so anomalous a 

 character, that if we were sure it is not due to some accident, we would have 

 regarded the species as the type of a new genus. 



Locality and position. Burlington, Iowa. Burlington Limestone. Collec- 

 tion of Mr. Chs. Wachsmuth. 



Poteriockinus sub- impressps. Body obconical. Base forming a shallow cup 

 about twice as wide as high, expanding moderately from the summit of the 

 column ; composed of plates which are about as high as wide, and pentagonal 

 in form, the angle at the middle of the upper side of each being a little in- 

 dented. First radials somewhat smaller than the subradials, wider than long, 

 pentagonal, or some of them hexagonal, and truncated above for the reception 

 of the second radials. First anal or sub-anal plate, a little larger than the 

 basal pieces, pentagonal, and resting between the upper sloping sides of two 

 of the subradial pieces ; second anal piece of the same size as the first, hex- 

 agonal in form, and resting upon the upper truncated side of one of the sub- 

 radials, while its left side connects with one of the first radials, and its right 

 with one side of the first anal piece, and with a third hexagonal piece resting 

 upon it. (Succeeding parts unknown.) 



The column is comparatively strong at its connection with the base, near 

 which it is composed of rather thin segments, connected by crenulated sutures; 

 its central perforation is of moderate size and pentagonal. 



The surface seems to be granulose, and the subradial pieces show a very 

 slight tendency to develope 9hort costce near the sutures on each side, and 

 below, as well as sometimes at their connection with the first radials above. 



The round indentations at the angles of the subradial and first radial plates, 

 present a rather marked character in this species. 



Locality and position. Burlington, Iowa. Burlington Limestone. Mr. 

 Charles Wachsmuth's collection* 



Poteriockinus tenuibrachiatfs. Body small, calyculate, or turbinate below 

 the summit of the first radial plates. Base small, forming a low pentagonal 

 saucer-shaped cup, composed of small plates, showing a pentagonal outline 

 above the column. Subradial plates rather large, about as wide as long, three 

 hexagonal, and two on the anal side heptagonal, and a little longer than the 



[June, 



