NATURAL SCIENCES OF PHILADELPHIA. 155 



A. ovaius, A. securus, A. opusculus, A. excerphis, A. infrequens, A. t/uilia, A. the- 

 tis, A. tfioas, A. locellus, A. sexarmatus, A. reiiculalus, all described under Ac/i- 

 nocrimis by Prof. Hall. Also, A. Fosleri and A. Ilurdianus, McChesney, and our 

 A. longus of this paper. 



It is worthy of note that all the known Burlington species of this group came 

 from the Lower Burlington beds, as has been determined by Mr. Wachsniuth, 

 by careful observations continued through many years. 



ACTINOCRINITES. Section (a). 



ACTINOCRINITES PENICILLUS, M. & W. 



Body small, inversely campanulate, or with sides expanding rapidly from the 

 truncated base to the secondary radius, which with the brachial pieces curve 

 a little outward. Base much depressed, or about four times as wide as high, 

 broadly truncated and but slightly concave below; margin more or less ex- 

 panded horizontally, and deeply notched at the sutures. First radial plates 

 comparatively rather large, and about twice as wide as high. Second radials 

 near half as large as the first, about twice as wide as high. Third radials a 

 little larger than the second, wider than long, and pentagonal iu form, the 

 lateral margins being short, each supporting on each of its superior sloping 

 sides a secondary radial of about its own size, which in its turn supports two 

 free arms. 



Anal pieces unknown above the second range ; first one smaller (particu- 

 larly narrower) than the first radials, and supporting two others of its own size 

 in the next range. Interradial pieces three to five in each space ; first one as 

 large as the second radials, hexagonal in form, and bearing upon its upper 

 sloping sides two smaller pieces, above which there is generally one or two 

 minute pieces. 



Arms free from their origin on the secondary radials, and composed below 

 of slender rounded pieces, the first of which is about twice as long as wide, 

 and more or less constricted in the middle ; beyond this the lateral arm on 

 each side of each ray is simple, with its second piece like the first, and fol- 

 lowed by two or three other shorter wedge formed pieces before passing into a 

 double series of small, alternately arranged pieces. Inner arms of each ray 

 bifurcating on the first piece, and one of the subdivisions in one or both bifur- 

 catiHg again on the first piece, thus making from seven to eight arms to each 

 ray, or from thirty-five to forty in the entire series. The single piece below 

 and the first above each division, is slender, rounded, and more or less con- 

 stricted, and generally two or three wedge formed pieces follow the latter be- 

 fore the commencement of the double series of alternating pieces, above which 

 the arms are a little wider and of moderate length. Vault unknown ; probos- 

 cis very slender at the upper end, and apparently of about the same length as 

 the arms. 



Surface of all the body plates deeply excavated at the corners, and promi- 

 nent in the middle, the prominence of the first radials usually forming a 

 transverse ridge, from which a single more or less defined vertical ridge as- 

 cends the second radials to the middle of the third, from which it bifur- 

 cates and continues to the secondary radials. 



Height of body to the top of secondary radials, about 0-22 inch; breadth at 

 the top of secondary radials, 0-40 inch ; length of arms if straightened out, 

 about 0-*?0 inch; breadth of do. at the widest part near the middle, 0-05 

 inch. 



This little species is allied to A. lucina, Hall, which, before seeing specimens 

 showing the arms, we had supposed to belong to the A. multibraehiatiis group, 

 but which is a true Actinocrinites. Our species differs, however, in having 

 the arms more frequently and ditferently bifurcating, so as to make from 

 thirteen to fifteen more in the entire series. Its arms also difier in not being 

 subspinous on their margins. 



1869.] 



