HAMBACH — NEW PALAEOZOIC ECHINODERMATA. 549 



Making due allowance for the crushed condition of the speci- 

 men, I estimate the vertical height to be 3 or 3!^ inches ; trans- 

 verse diameter, about the same or a very little more ; width of 

 ambulacrum, li inch; width of interambulacrum, |ofan inch. 



The species is readily distinguished from Melonites multipora 

 in being throughout of a coarser structure ; interambulacral 

 areas composed of five rows of plates instead of from seven to 

 nine ; by having a more prominent ridge in the centre of the 

 ambulacrum, and being also covered with larger spines. The 

 number of interambulacral plates would alone be sufficient to 

 separate it from Melotiites multipora^ as well as Stewarti Saf- 

 ford, which, after a careful examination of a good cast from the 

 original specimen, I have to regard as synonymous with multi- 

 pora — a conclusion arrived at after an examination of over 500 

 specimens, which proved that the number of plates in the inter- 

 ambulacrum is never less than seven or eight, whereas the one 

 now described has only five in the greatest with of the field. 



Geological formation and locality — In the lower St. Louis lime- 

 stone, St. Louis, Missouri. 



Melonites irregularis, n. s. 



(PI. C, Fig-. 2.) 



Body globose. Ambulacral field not quite so wide as the inter- 

 ambulacral space. Poral plates very small and irregular in size ; 

 there are from three to five rows to each side of the central ridge 

 in the ambulacrum, which is very shallow. Literambulacral 

 space composed of small hexagonal and pentagonal plates, less 

 regularly arranged than in Melonites multipora and numbering 

 from five to seven in the greatest width. Surface ornamented 

 with coarse granulations, less numerous in the same space than 

 in multipora. Genital plates the same as in other Melonites. 



This species has the same general appearance as Melonites 

 multipora with the exception of its smaller size, but is readily 

 distinguished from the same by its smaller plates, both ambula- 



