A. II. COLE PAL-EASTER EVCHARIS, HALL. 513 



-In the collection there is an impression of a single ambulacra! area of this species, which is 

 spread open laterally, and measures about two and a half inches in length by nearly three-fourth a 

 of an inch in width in the middle, broadly petaloid in shape, and showing the form and number of 

 the poral plates, with the posit inn of the pores and their junction with the adambulaeral plates." 



The specimen in hand differs from this description in the following particulars : 

 The terminal <>r axillary plate of the marginal range is elliptical in form, with 

 its major axis directed toward the adjacent reentrant angle. Its surface is granuL isl- 

 and bears three short, thick, blunt pointed spines. The marginal plates bordering 

 each reentrant angle bear similar but more slender spines, which are not "as long 

 as the transverse diameter of the plates." The spines arc arranged in a row near 

 the distal margin of the plates and number five on the plates at the angle, the 

 number and size decreasing until they disappear at the sixth or seventh plate from 

 the angle. All the marginal plates are nearly smooth on the free margin and be- 

 come gradually more granulose toward the line of junction with the adambulaeral 

 plates. The margins of the rays show in three places that the ventral marginal 

 plates were visible from above, agreeing with the original description. 



The adambulaeral plates are apparently less numerous than stated in the original 

 description, and "the single minute plate" at the points of the pairs of the oral 

 plates is visible in this specimen and is armed with two relatively long, slender 

 spines which are apparently but a part of the full armature. The adambulaeral 

 plates, including the triangular oral plates, bear well defined spines, which are 

 shorter than the diameter of the plates to which they are attached. Each plate 

 bears two spines so near to the distal margin that the impressions of the short and 

 obtusely pointed spines frequently bridge the well defined groove between the 

 adjacent adambulaeral plates and terminate near the proximal margin of the next 

 plate. The spines decrease in size toward the end of the ray and a few plates show 

 only one spine. The plates of this range are thick, equaling two-thirds to three- 

 fourths the depth of the groove. The vertical angles of the faces forming the 

 lateral walls of the groove are beveled, so that lateral extensions of the groove are 

 formed between each two plates on the same side. These lateral expansions are 

 narrow and shallow at the oral surface, deeper and wider inward ; so that the faces 

 of the adambulaeral plates near their junction with the poral plates are reduced to 

 a narrow edge which projects inward and nearly touches the corresponding plate 



on the other side of the groove. The general appearance of the fossil as well as the 

 outline of the rays at the points where the broken block presents a transverse sec- 

 tion of them indicates that the plates have their normal position, not having 

 suffered distortion by pressure. 

 The ambulacra! plates are shown by a well defined mold of their under or 



external surfaces. The soft matrix which tilled the ambulacra! furrow pressed 



upon the membranes connecting the ambulacral plates and occupying their pur.-, 

 and as these membranes decayed it was forced by gentle pressure into the pores 

 and between the edged of the plates. The mold of the groove is less than one- 

 eighth of an inch in width in a ray measuring five-eighths at its base. The upper 

 Burface of the mold hear- a narrow longitudinal median ridge which marks the 

 junction of the two ranges of ambulacra! plates, similar transverse ridges, w hich 

 are continuous with the lines marking the junction of the inner faces of the 

 adambulaeral plates, mark the proximal and distal margins of the ambulacral 



plates. Theseridgesd t cross at a righl angle to the median line, but include 



between their proximal sides an angle of aboul 125°. These ridges indicate thai 

 the ambulacral and adambulaeral plate- were equal in number, and thai the former 



