115. CONTRIBUTION TO 



enough to deserve a name, coming from a horizon that has yielded little of 

 suc'li material. 



The base is pentagonal and ({uite large, forming a low cup or bowl. 



A row of more or less coalescing nodes passes from the stem base to each 

 angle of the pentagon and within the five triangles thus formed, four rows of 

 coalescing nodes run parallel to the baso-radial sutures (sides of the pentagon). 

 The nodes are strong and sharp. There is a bceak in the test at the base so 

 that tlie stem cicatrix can not be determined as to shape and depth. 



Middle Devonian, Falls of the Ohio. Collection of Mr. G. K. Greene. 



PEN T R E M 1 T ES O B E S U 8 , Lyon , Rowley. 



Plate 36. Figs. 1, 2-3. 



The specimen represented on our plate by figures ], 2, 3, though somewhat 

 inferinr in size to Lyon's type specimen, is a fine individual, and preserved in 

 such a way that every plate suture can be readily made out. 



It ditfers from the drawings in the old Kentucky report, mainl} in the 

 shape of the body above the ambulacral tips, where the greatest width occurs, 

 thus giving little curvature to the lateral outline. 



Below the ambulacral tips the body has less height, and the lateral bound- 

 ing lines curve inward instead of being straight as in the specimen with which 

 we are making the comparison. 



The cliief characters of P. obesus seem to be its great size, rather strongly 

 convex base, strongly lobed character of the fork pieces, the deeply sunken 

 anibiilacra, themselves trough-shaped; the great height of the bounding edges 

 of trie fork and deltoid pieces above the ambulacra, and the high, acute upper 

 points of the deltoids, extending much above the ventral surface. The del- 

 toids iheniselves are rather large and separated below from the fork pieces by 

 curved sutures. The central opening (uncovered ventral region) is small, and 

 the four spiracles and anal opening are but medium in size. A long triangular 

 depression with the radio-deltoid suture as a base, has its vertical angle below 

 the middle of the radial edge, bounding the ambulacrum. The two of these 

 triangles in an interambulacral space, together with the dekoid at their bases, 

 form a slightly depressed inverted v-shaped area. This character is common 

 to many blastoids and not confined to the genus Pentremites. In LophohlaHtiiH 

 i'lKiji/natn.H it is sometimes so strong as to give rise to a spine-like elevation in 

 the forlc pieces at the union of the radial and radio-interradial sutures. 



Ttie edges of the fork pieces bounding the ambulacra are often irregular, 

 lluted or thrown into folds and depressions, giving rise to spine-like processes 

 us in Dr. Hambach's species P. ,'ipf'nosu,s, and doubtless to the nodosities in 



