190 



PALEONTOLOGY OF NEW-YOEK. 



584. 3. THYSANOCRINUS ACULEATUS (n. sp.). 



Pl. XLII. Fig. 3a-d. 



Fingers composed of a double series of alternating joints, slightly interlocking upon the 

 back ; first joints of the tentacula alternating with the joints of the fingers, short, pentagonal, 

 not diminishing towards the outer extremity ; second joints of tentacula elongated, twice as 

 long as the first joints, and gradually narrowing to their junction with the third joints. The 

 first two or three joints rounded, smooth or finely granulated ; third or fourth and succeeding 

 joints grooved longitudinally ; number of joints in each tentacle not ascertained. 



This species presents a striking contrast to either of the preceding, in the first short joints of 

 the tentacula, which partially alternate with the joints of the fingers ; the two sides, thus in 

 contact with the finger joints, being about equal to one-third on the upper and two-thirds on 

 the lower of the two joints in contact. When closed, the back of each finger presents a de- 

 pression along the suture, which is quite conspicuous, and differs from the preceding species. 

 The first two or three joints are smooth or granulated, without ornament. On the third, or 

 sometimes only on the fourth joint, commences a shallow groove, on each side of which the 

 surface is rounded. 



The degree of alternation of the tentacular joints with those of the fingers is slightly variable ; 

 and in some positions of the fingers, this character may be overlooked. 



When once understood, the characters of the finger and tentacular joints of the three pre- 

 ceding species are as clearly defined and reliable as the characters derived from any other part 

 of the crinoid. The single joints of the tentaculum, though scarcely visible to the naked eye, 

 become, under the magnifier, marked by distinct and reliable characters. 



From the similarity in general features and arrangement of parts, the two preceding species 

 are referred to the same genus with figure 1, though no other parts of the animal have been 

 seen. The name of this species is given from the aculeate second, or second and third joints 

 together, of the tentacula (see fig. 3 c). 



Fig. 3 a. The upper part of a crinoid, showing the contracted fingers and tentacula, five of 



which are seen in the figure. 

 Fig. 3 b. An enlargement of the back of a part of one of the fingers, showing the joining of the 



plates. 

 Fig. 3 c. Several joints of the finger enlarged, showing the tentacula attached, the form, etc. of 



the joints. 

 Fig. 3 d. Several joints from another individual enlarged, showing the first joints of the tentacula 



to be less extremely alternating than in fig. 3 c. 



Position and locality. In the shale at Lockport. 



