104 



characters. A simple contraction produces on every plate a nearly pointed star- 

 like figure, each ray being directed towards the sides. A partial contraction 

 extends the points of the rays, and a very powerful one forms a continuation 

 of the rays of the star on one plate, extending with an equal thickness to 

 the adjoining plate. It is this degree of contraction which permits our tracing 

 the direction which thr muscles pursue in acting on the arms and capital plates, 

 as may be fully seen in a fine specimen in my collection. (PL. n. fig. 1.) The 

 divided action from the three adhering joints of the pelvis produces two folds, 

 directed to the centre of the first costal plates, (resting upon the lines of their 

 sutures) ; here it unites and proceeds over the second costal to the centre of the 

 scapula, where the muscle divides and attaches to the first joint of each hand. 

 Another fold extends laterally on each side from the centre of the first costals 

 across the intercostalsnear it, to the first fingers of the opposite arms, each again 

 dividing at the second intercostals, and sending branches to the pectoral plates. 

 Other rays decisively point out lateral action. Another specimen in my col- 

 lection, shows the ridges produced by contraction slightly waved, (PL. IT. fig. 3.) 

 whilst a third specimen (PL.n. fig. 4.) exhibits two or three ridges, according 

 as the costals traversed by them are inserted over the suture of the pelvis, or 

 over the middle of its plates, sending double folds to each of the two lateral 

 angles, and producing a corrugation in the centre of the costals. 



The PECTORAL PLATES (PL. n, fig. 7. to 14.) do not contract into a simple 

 tubercle, but form an elongation dividing at its summit into several points. 



The first FINGER sets off from the outside of the cuneiform joints of the arm, 

 and the continuation of the hands consists of two or three series, each contain- 

 ing two common and one cuneiform joint, and terminating in three or four 

 fingers. 



The proboscis-like mouth, is capable of very considerable elongation, as is 

 shown in the fine specimen figured by LHWYD : by the obliging kindness of the 

 Rev. Professor BUCKLAND, I have been enabled to examine and refigure 

 it(PL. i.fig.2.) with a more careful attention to those anatomical details to which 

 I have particularly directed my inquiries in investigating the history of these 

 animals. 



I am indebted to the polite attention of the Rev. R. HALIFAX, (with whom I 

 made an excursion to the Mitcheldean Limestone Basin) for several detached 



