NIAGARA OBOUP. 217 



resting partly upon the upper edges of the scapulars and partly upon the base of the arms, 

 having on one side a mouth composed of six small triangular plates forming a little conical 

 elevation ; arms thirteen (the number sometimes variable), composed, from near the base up- 

 wards, of a double series of slightly interlocking joints, which are sharply tuberculated on their 

 surface and intermediately granular, a kind of foliaceous tentaculum attached to their inner 

 margins ; tentacula with numerous oblique joints, which are narrow at their bases, and gradually 

 expand on each side of a central line or midrib ; surface of the plates of the body marked by 

 striae or rows of granules parallel to their edges, sometimes by tubercles irregularly arranged 

 and more or less abundant ; all the plates to the centre of the scapular plates marked by 

 single or double rows of pores, which proceed from the base of the pelvic plates to the 

 prominent upper angles, and from the basal angles of the costal plates to their centre, 

 whence they radiate to each of the upper angles of the same plate, meeting corresponding 

 rows from the centre of the scapular and interscapular plates. These pores communicate with 

 the interior, and, though not always conspicuous, are present in some degree of development 

 in every individual. The plates of the summit partake of the same variable character in their 

 surface markings, as those of the body below. 



This very interesting crinoid combines within itself, in its numerous phases, the elements of 

 many interesting developments, which become important characteristics in other forms of this 

 class of animals. 



M. VoN BucH has given a very elaborate account of this species ; and it is quite evident 

 that he has examined numerous specimens, to have seen all the phases which he describes : 

 nevertheless there are some points in which our specimens present characters either not observed 

 by him, or not described as we understand them*. 



It will be seen from the date of Say's description, that this species has been a long time 

 known, and for many years it was almost the only crinoid well ascertained in this country. 

 The immense numbers which were found at Lockport, about the time Mr. Say described this 

 species, placed it within the reach of every one, and they were to be seen in every collection! . 



*M. Von Buck gives the author credit for having given (Geol. Rep. 4th District) the best figures of this fossil 

 yet published, though without a description ; and yet he says that many parts have been misunderstood, or inac- 

 curately represented ! It will be perceived that the present description does not, in some particulars, correspond 

 with that of M. Von Buck, though it does with numerous specimens in the author's collection. By comparing 

 the two, it will be observed that some points have escaped the attention of this very careful observer himself; and 

 if the specimens figured in the Geological Report are compared with the figures there given, no great inaccuracies 

 will be found in any parts represented. The smaller specimen there given is remarkable for the irregularity in the 

 pores of the costal plates, and the occurrenoe of interrupted double rows from the centre obliquely to the basal 

 angles. At the time when the figures of the interior of the costal plates were given (Tables of Organic Remains No. 

 ] 9, figs. 5, 6 and 7 at the end of volume cited), showing the distribution of these pores, and their connexion with the 

 internal structure of the animal, as now described, the author supposed they could be understood without the aid of a 

 description. 



t This period was at the time of the excavation for the Erie Canal, when these crinoids were found in immense 

 numbers at Lockport, from which place Mr. Say's specimens were obtained. Many hundreds, and probably thou- 

 sands of individuals, were obtained at that time ; and one gentleman informed me, that at one time, he had half a 

 bushel of them. In all the specimens which I have seen, collected at that period, not one possesses the fragment of a 



[Palaeontology — Vol. ii.] 28 



