NATURAL SCIENCES OF PHILADELPHIA. 83 



in the specimen illustrated by us are the oral and adjacent pieces acci- 

 dentally pushed upward, and seen from the upper or inner side after the re- 

 moval of the dorsal side or covering ; and that the central opening is the 

 oral aperture. At an}' rate we know of no other way to account for the 

 very diiferent appearances presented by these fossils, when examined in different 

 conditions. 



Since we have had some specimens of this type at hand which we have felt 

 at liberty to grind and cut into, so as to reveal more clearly their structure, we 

 find that the arm-pieces, which in the denuded specimen first examined by us 

 presented the appearance of becoming isolated, deeply furrowed lanceolate 

 pieces, at a little distance from the body, and of very little thickness or depth, 

 really appear, when ground ofi', to extend nearly all the way down from the 

 dorsal to the ventral sides of the arms, and to be connected and articulated 

 together, like those nearer the body by little processes and sockets; the com- 

 paratively thin furrowed dorsal edges becoming thicker farther in. 



Sometimes these arm-pieces appear as if consisting of two rows joined in 

 pairs at their inner ends along the middle of the dorsal side, there being a 

 rather large pore (or possibly only a deep pit) at the junction of the two pieces 

 forming each pair. In other instances, as seen detached, these pairs of pieces 

 are found to be firmly anchylosed so as to form single pieces, extending 

 across the whole breadth of the arms, without, however, obliterating the ap- 

 pearance of a rather large mesial dorsal pore. 



We have not yet had an opportunity to see the under side of the body or 

 arms in any of the Crawfordsville specimens, but Mr. Wachsmuth has a speci- 

 men from the Burlington division of the Lower Carboniferous beds of Bur- 

 lington, which would seem to belong to this genus, though specifically distinct.* 

 This is the form Prof. Hall has described in some preliminary notices of fossils 

 (issued at Albany, N. Y., in 18G1), under the name Prolaster? Barrisi. This 

 fossil has, so far as we have been able to see, essentially the same structure, 

 and shows along the under side of the arms a broad shallow depression in the 

 arm-pieces, somewhat like an ambulacral furrow. None of the specimens of 

 either species we have seen show any indications of any proper extended disc, 

 the body being comparatively small. It also evidently differs in several points 

 of structure from Frotaster. 



So far as its structure is yet known, it seems to be a true Ophiurian. We 

 only know the species, Onychaster Jiexilis. 



Remarks on the BLASTOIDEA, with Descriptions of New Species. 



BY F. B. MEEK AND A. H. WORTHEN, 



Of the Illinois State Geological Survey. 



In regard to the nature of the functions for the performance of which the 

 openings in the summit of this group of fossils, as the specimens are usually 

 found, were designed, authors do not entirely agree. The central opening has 

 been most generally regarded as the mouth, and the others surrounding this 

 (excepting one that is always larger than the others) as ovarian apertures ; 

 while the larger one is usually supposed to be the anal aperture, with, in some 

 types, two of the supposed ovarian apertures opening into it, one on each 

 side.f 



*We have not yet, however, seen any of the little articulating knobs on the scales of 

 this Burlington species. These impart the granular appearance to the surface of our 

 typical species, in which each scale has one of these little knobs articulated in its middle. 

 If the Burlington species did not have these, it may belong to another, but allied genus. 



f In the genus I'eiUremites, as specimens are usually found, there are live of these open- 

 ings of the summit, surrounding a central pentagonal aperture. Of these live surround- 

 ing openings, four are known to be divided within into two each, and the lifth one into 

 three, the middle one of these three being generally supposed to be the anal opening, 



1869.] 



