ROOM II. PENTREMITES. 89 



dredged up from the bottom of the sea. The reduced sketch 

 of a small portion will serve to convey an idea of the elegant 

 forms of these petrified zoophytes of the Jurassic ocean ; 

 the contemporaries of the Ichthyosauri and other marine rep- 

 tiles, of which we shall treat hereafter. The Pentacrinites 

 on this slab are for the most part entire ; the peduncle being 

 affixed to the base, and the column extending upwards in gen- 

 tle undulations, and supporting the receptacle, which has the 

 arms gracefully outspread in various attitudes*. The struc- 

 ture of the receptacle, and of the arms, and the extreme deli- 

 cacy of the finer tentacula made up of countless minute 

 ossicula, are admirably shown in this unique and most 

 instructive specimen. 



This Case also contains illustrative examples of the Actino- 

 crinites (Nave Encrinite), 1 Cyathocrinites (Cup Encrinite), 2 ^- 

 geniacrinites (Clove Encrinite), and several other genera. 



Pentremites. One peculiar type of Crinoidea requires a 

 brief notice, as it was supposed to be without arms, and to form 

 a connecting link between the lily-shaped zoophytes and the 

 sea-urchins. The Pentremites has a receptacle supported by 

 a short pedicle, and composed of polygonal plates, divided by 

 five perforated grooves or furrows, which are of an elongated 

 petalous form, and converge in a rosette on the summit. 

 The marginal longitudinal rows of minute pores are not how- 

 ever for the passage of soft membranous feelers, as in the 

 ambulacra of echinoderms, as was formerly conjectured, but 

 are channels for the transit of vessels that supply an infinite 

 number of delicate simple tentacula, composed of extremely 

 minute calcareous ossicula, as in the other Crinoidea, but not 

 subdivided as in the Pentacrinites -and Encrinites. These 

 tentacula are directed upwards towards the vertex of the 

 receptacle, and are supposed to have been organs for seizing 

 and conveying food to the mouth. 3 



These Crinoideans abound in the mountain limestone, 

 especially in some districts of the United States, where certain 

 strata are distinguished by the name of pentremital limestone. 4 



1 "Medals of Creation," p. 324. 2 Ibid. p. 326. 



3 See Dr. Fred. Roemer on Jointed Tentacles found on the ambulacra! 

 spaces of Pentremites, " Geol. Journal," vol. v. p. 8. 



4 "Medals of Creation/' p. 327. 



