INVERTEBRATES . 177 



this genus, the arms of which have been discovered, is C. bullosas, Hall (Fif- 

 teenth Report Regents Univ. N. Y., p. 123, pi. 1. fig. 19-20), from the Upper 

 Helderberg rocks. In this the hemispherical or bulb-like body is extremely 

 small compared with the remarkably robust arms, which are long, spread out 

 horizontally, and bifurcate several times without diminishing in size, so that it is 

 manifest they could not have been capable of being raised into an erect or ver- 

 tical posture, and folded together like those of most other palaeozic crinoids. 

 Indeed it seems difficult to conceive how an animal with so small a visceral 

 cavity, could have been endowed with sufficient muscular and nervous force, to 

 move such ponderous arms with any degree of facility. Hence it is probable 

 that during the life of the animal, its arms were always extended out horizon- 

 tally, and spread upon the same plane, like the rays of a fan. From all its 

 known characters, we therefore regard it as the type of a distinct little group 

 from the typical forms of Cyathocrinus, notwithstanding its agreement with 

 that genus in the structure of the cup. For this group we would propose the 

 name Arachnocrinus, from the spider-like appearance of the body and extended 

 arms. In addition to the typical species A. hulbosus, it will doubtless include 

 A. pisiformis=( y Poteriocrinus pisiformis, Roemer), and some other Upper Silu- 

 rian species. 



In the August (1855) number of the Proceedings of the Philadelphia Acad- 

 emy of Natural Sciences, p. 159, we proposed the name Eupaciiycrinus, 

 (eu, well; Ttaywz, thick; xpcvov, a lily), for the reception of a curious 

 group, the type of which was figured by Mr. Lyon, in the Kentucky Geological 

 report, vol. iii, pi. 1, figs. 2,2 a and 26, under the name Graphiocrinus li-bra- 

 chialis. As little is known of the upper part of the body of this crinoid, it 

 is difficult to determiue whether it is more nearly allied to Poteriocrinus, or to 

 Cyathocrinus. It differs from both, however, as well as from Graphiocrinus, 

 in having its arms, from their origin on the first piece after the division on the 

 second radial plate, composed of a double series of minute, very short, inter- 

 locking pieces, as well as in the remarkably solid, tumid character of its body 

 pieces. For the present we place this group provisionally as a section of 

 Cyathocrinus, though it is quite probable it will be found generically distinct 

 both from that genus and Poteriocrinus. In addition to the typical species, it 



Note. — Since writing the above, a comparison of Mr. Lyon's figures of his G. 

 li-brachialis, in the Kentucky Report, with deKoninck's figures of his genus Hydreiono- 

 crinus Woodianus {Bull. Acad. Roy ale de Belgique, pi. ii), leads us to suspect that 

 the Kentucky fossil, as well as the other species mentioned above, may possibly fall 

 into Prof. deKoninck's genu's. If so, of course the name Ifydreionocrinus will have to 

 take precedence over Eupaciiycrinus, and the group could not be placed as a subgenus 

 under Cyathocrinus. Until more is known in regard to the upper parts of these Amer- 

 ican forms, however, this must remain an open question. 

 23 Aug. 30, 1866. 



