896 PROCEEDINGS OF THE ACADEMY OP 



the head, 0*17 inch ; diameter of head, 0-22 inch ; length of lateral spinules, 

 0-10 inch. 



Locality and position. Liberty, Randolph county, Illinois. Upper bed of 

 Chester Limestone. Lower carboniferous series. 



Genus'PAL^CHINUS, McCoy. 



PaljECHinits Burlingtonensis. The only specimen of this species we have 

 yet seen is too imperfect to show the exact form of the entire fossil, though 

 it seems to have been nearly spherical. It has four to five ranges of interam- 

 bulacral plates near the middle of each area, and they decrease in number to 

 three, two, and apparently at last to one at each extremity. The inner pieces 

 are wider than long, and regularly hexagonal, excepting near the upper and 

 lower extremities of the spaces, where they are about as long as wide, and 

 occasionally pentagonal ; those of the outer ranges are all pentagonal, their 

 outer margins being truncate, and crenulated for the reception of the small 

 ambulacral pieces. 



The ambulacra are narrow, or about as wide as the first range of interam- 

 bulacral plates on either side, slightly convex along the middle, and a little 

 concave at the margins. They are composed of a double alternating series of 

 very small pieces, which are two or three times as wide as long ; about five to 

 seven of them equalling the height of each contiguous interambulacral 

 plate. They are each pierced by two small rounded pores near the outer 

 margin, and all of nearly uniform size towards the extremities of the 

 ambulacral areas, but in the central or widest part they become alternately 

 wider at the inner and outer extremities ; those having their narrower end 

 outwards often wedging out to a point between the others before reaching the 

 margin of the ambulacral space. 



The surface of all the plates is ornamented by numerous regularly arranged 

 granules, two of which occupy the inner half of each ambulacral piece. 



As near as can be determined from our specimen, it must have been, when 

 entire, not less than 2'25 inches in length, and about 2 inches in breadth. 

 The largest interambulacral plates are 0'19 inch wide, and - 17 inch in height ; 

 breadth of widest part of ambulacra. 



Locality and position. Burlington, Iowa. Burlington Limestone of the lower 

 carboniferous series. 



Genus MELONITES, Owen and Norwood. 



j t 



All the published figures of Melonites multipora, the type, and hitherto the 

 only known species of this genus, give a very incorrect idea of the form and 

 arrangement of its ambulacral pieces and pores. The three lateral series of 

 these pieces on each side of the two middle ranges, instead of being as repre- 

 sented, composed two of quadrangular, and one of pentagonal pieces, placed 

 in oblique transverse rows, and mounted one upon another so as to form at 

 the same time regular longitudinal ranges, are made up of irregular alter- 

 nating unequal pieces of various forms. They are also wedged in between 

 each other in such manner, and so interrupted by small intercalated pieces, 

 not properly belonging to either range, that it becomes very difficult to deter- 

 mine whether we should count them as four or as five rows, on each side of the 

 mesial suture ; or, in other words, as eight or ten rows to each ambulacrum. 

 The same irregularity also occurs in the pores, which are round, in closely 

 approximated pairs, and not arranged in regular longitudinal or transverse 

 lines, but so as to show a tendency to assume a quincunx arrangement. 



Should the gemis of Polypi, to which Lamarck first applied the name Melonites, 

 be retained, it will become necessary to give another name to the group now 

 under consideration, in which case we would propose to call it Melonechinus. 

 Although related to Palazchinus of McCoy, this genus is clearly separated by 

 the numb er and arrangement of its ambulacral pieces and pores, as well as by 



[Sept. 



