PAL^ONIOLOGICAL EEPOET OF GEOLOGICAL SURVEY. 491 



common origin opposite the pores ; these are divided by grooves of un- 

 equal depth, increasing in size and depth from the origin of the ridges 

 to the bottom of the groove, quite analogous to the same part in Pen- 

 tremites obesus. 



The pores communicate with the interior of the body. On either 

 side the pore pieces are supported by a piece, two to each field, ten in 

 all, of equal width, nearly of the same form, ornamented with grooves 

 and ridges. The grooves rise at a pore, and cross the pieces transversely, 

 and terminate against the interradial pieces, the whole surface of the 

 pieces being covered by grooves and ridges, which are equal in size to 

 the pore, or the division between the pores, against which they severally 

 originate. These are again crossed obliquely from the outside of the 

 pieces upward, by a set of ribs which rise against the interradials and 

 anal piece, and cross the' supporting pieces of the pseudambulacrse. 



The summit within the circle of the large pores (ovarian openings ?) 

 is divided into about twenty-two small pieces, six of which are dis- 

 posed around the seventh, -which occupies the centre of the crown. 

 They are nearly of equal size, polygonal or nearly circular; without 

 the line of the six pieces, and falling into the indentations around the 

 circle formed by them, are smaller pieces, and on either side of the 

 outer circle of the ovarian (?) openings are small linear pieces, abut- 

 ting against the small pieces outside of the first circle ; all the pieces 

 exept the linear ones are studded with a number of small prominent 

 granules. 



Specimens of this fossil are found ranging from . T 3 -g\ in inch, to an 

 inch and .^\ in length. 



The relative proportion of one of the medium sized, rather globose 

 specimens is as follows : 



Greatest length, 1.^- inches. 



Length from bottom of columnar-pit to summit, I-tVo inches. 



Greatest diameter, 1-tVt inches. 



Least diameter, 1.jl?_ inches. 



Length of second primary radials, - - - .-A- 5 _ inch. 



Length of first primary radials, - - - ._o_ i nc h. 



Length of basal pieces, .... __oj>_ ^^ 



Greatest length of the pieces, - - . l._?_o_ inches. 



Greatest width of pseudambulacral fields, - .^S- inch. 



