FOSSILS OF THE BURLINGTON GROUP. 475 



central opening in the specimen illustrated by us are the oral and adja- 

 cent pieces accidentally pushed upward, and seen from the upper or 

 inner side after the removal of the dorsal side or covering, and that the 

 central opening- is the oral aperture. At any rate we know of no other 

 way to account for the very different 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 speci- 

 men first examined by us presented the appearance of becoming isola- 

 ted, deeply furrowed lanceolate pieces, at a little distance from the 

 body, and of very little thickness or depth, really appear, when ground 

 off, 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. Ivy little processes and sockets ; the comparatively 

 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 de- 

 tached, 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 appearance 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. WACH- 

 S^IUTH has a specimen from the Burlington division of the Lower Car- 

 boniferous beds of Burlington, 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, IS". 

 Y., in 1861), under the name Protaster ? 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 evi- 

 dently differs in several points of structure from Protaster. 



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

 "We only know the species Onychaster flexilis and 0. Barrisi. 



* We have not yet. howcviT. seen any of the little articulating knobs on the scales of this Burling- 

 ton 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 

 n ave these, it may belong to another, but allied genus. 



