186 UPPER, OR FLINTY CHALK. 



traversed by a longitudinal ridge, with a minute depression in the centre, 

 and is adapted for the reception of the clavicles. 



The clavicles are small, and of a semilunar form externally ; the upper 

 edge is thick, nearly straight, and unites with the humerus ; the lowermost 

 is rounded, and corresponds with the semilunar cavity of the scapula ; be- 

 tween these two svu-faces, on the inside, is a triangular space, the use of 

 which is not at present known. 



The cuneifo?'m or humeral bones, may be considered as the first of the 

 arms ; they have four articulations, and are attached to the clavicles by 

 the two lowermost. Their upper margin forms two oblique surfaces, each 

 divided by a longitudinal ridge, in the same manner as the first joint of the 

 finger in the Bradford encrinite {apiocrinites rotundus). From this struc- 

 ture it may be inferred, that the arms were dichotomous, but whether 

 they were subdivided, and terminated in elongated tentaculae, as in the 

 crinoidea, cannot be ascertained, since none of the specimens contain any 

 vestiges of the ossiculae of these appendages. On the inner surface of the 

 humerus, a smooth space is observable, appearing hke a continuation of the 

 triangular interval, on the corresponding part of the clavicle : is this the 

 articulating surface for the attachment of the pectoral bones ? 



The reniform ossiculcE, or pectoral bones, are united to each other by 

 their upper and under surfaces, both of which are divided by a ridge into 

 two depressions. In the only specimen, (Tab. xvi. fig. 6.) in which these 

 bones remain, the respective parts have suffered so much displacement, 

 that their mode of arrangement is no longer distinguishable; there is, 

 however, reason to conclude, that in the recent animal they were attached 

 to an epidermis extending over the cavity of the pelvis in the form of a 

 proboscis, the mouth being placed in the centre. 



From this examination of the skeleton of the marsupite, it is evident 

 that the recent animal was nearly related to the crinoidea ; but the ab- 

 sence of the vertebral column separates it most decidedly from that tribe. 



It may however, as Mr. Miller observes, be considered as forming a 

 link between the crinoidea articulata and the stelhridce. 



The folds, radiating ridges, and stria3 on the plates, and the lateral 



