DESCRIPTIONS OF SOME NEW RLASTOIDS. 9I 



variety or more adult phase of the above species. Hall describes the 

 latter as more expanded in the upper part of the body, with the base 

 proportionally narrower, and this agrees with our s])ecies; but the body 

 is comimratively longer than in Hall's smaller type, while it should, if 

 representing the adult form of the other (according to Wachsmuth, 

 see the i)receding paper), on the contrary, be wider and not higher. 

 In Ehvac7'inus luciria the basals are almost on a plane with the radials, 

 and the ambulacra touch the bottom, which is not the case in E. obo- 

 Tafiis; in tlie former the lower truncate portions are much wider, and 

 the basals, instead of being deeply concave, are jMovided with an 

 elongate node in the center. 



The above description was made from ten specimens of all si/es; the 

 largest one measunng one inch and three-quarters in length, the smallest 

 seven-eighths of an inch. 



Geological position^ etc.: Found in the shales of the Hamilton group 

 at Buffalo, in hmestone of the same age, at Iowa City, and at the top of 

 the Hamilton grou[i in the Thunder Bay region of Northern Michigan. 



The original specimens are in the collection of Mr. Charles Wachs- 

 muth and in my own. 



El^acrinus mei.oniformis Barris, Nov. sp. 



Plate I. — Fig. 3. X'ential aspect of a specimen. 



Body small, ovoid, height nearly one-half more than the width ; 

 greatest width through the median jiart, or a little above; curvature 

 toward the two poles nearly e(iual, l>ut the pole itself at the al)actinal 

 side abruptly depressed, and the concavity perfectly filled by the 

 column. Surface of the ambulacra raised but little above the general 

 plane of the body. The jilates along the sides of the ambulacra are 

 marked with obscure transverse grooves, bordered at each side by a 

 sharp ridge, which forms along the median portions of the plate a 

 deltoid-like figure. The ridges which join with one end at the summit, 

 with the other at the radial lips, form together around the body a well- 

 marked penta-petaloid figure, in which the ambulacra are placed along 

 the median line; and as the ridges in this species happen to be more 

 conspicuous than the margins of the ambulacra, the ridges appear as 

 the boundaries of the latter. Cross-section along the upper half of the 

 body obscurely decagonal, almost circular, decidedly pentagonal across 

 the lips of the radials. 



Basals small, entirely hidden within the columnar cavity. 



