438 PALAEONTOLOGY OF ILLINOIS. 



furrow within. Minute ambulacral pieces extending up 

 the furrows of the arms, from five to seven to each arm- 

 piece in each row, the two rows arching over the deep fur- 

 rows. Proboscidiform ventral tube very long, slender, 

 cylindrical, and composed of apparently not more than 

 two or three vertical ranges of oblong curved pieces, about 

 half as long as those of the arms. 



Column comparatively rather stout, rounded, and com- 

 posed near the base of more or less irregular pieces, gradu- 

 ally becoming thicker farther down, and all pierced by a 

 small rounded or subpentagonal central canal. 



Surface, when well preserved, showing under a strong- 

 magnifier minute granulations, with a tendency to run to- 

 gether into a kind of vermicular style of marking. 



Hight of body of a medium sized specimen, to the top 

 of the first radial pieces, 0.16 inch; breadth, 0.28 inch; 

 hight to top of second radial pieces, 0.30 inch. Length of 

 arms, about 3 inches; breadth of same at the base, 0.15 

 inch. Thickness of column, 0.10 inch. 



This species will be at once distinguished from all the others known 

 to us, by having its body obtusely rounding under to the column below, 

 instead of expanding upward from the same, with straight or concave 

 sides. By this character alone of its body, exclusive of the second ra- 

 dials, when found detached, it can readily be distinguished from S. 

 dentatus, Owen and Shumard, as well as from S. Wortheni and S. papil- 

 latus. Hall. 



We have elsewhere noticed the occurrence of a long pipe-stem-like 

 ventral tube in this genus, and a double series of minute ambulacral 

 pieces extending up, and apparently arching over, the ambulacral fur- 

 row of each aim.* These characters were first observed in this species, 

 in which the ventral tube seems to be nearly as long as the arms. We 

 have also seen indications of the same characters in S. Wortheni, and 

 fragments of other undetermined species, and hence have little doubt 

 that they occur in all the species of the genus, when well preserved. 

 There is perhaps scarcely any other type of all the various genera of 



* Sometimes these pieces are thrown apart along the middle, as if they had been movable and ar- 

 ticulated so as to open or close together over the ambulacral furrows. So far as we have been able to 

 see there would appear to be no pinnulae in this genus. 



