14 BULLETIN OF THE 



each other and united by ligament, except at the extreme end, where 

 there is a small space in which the cartilages appear to have coalesced. 

 They approach each other in an angle of about forty-five degrees. The 

 scapula is less angular and more slender ; at its upper end there is an 

 elongate flexible segment. 



The metapterygium (mtp) of the pectoral is about half as long as the 

 fin itself; it is slender, broader backward, tapered in front and articu- 

 lates by a small surface with the coracoid. It is in two segments, and 

 bears two radials at the end and ten on the side. 



The mempterygium (msp) is a large triangular plate extending upward 

 in an angle between the propterygium and the radials, but not sepa- 

 rating the metapterygium from the coracoid, as in the sketch; it articu- 

 lates with the process in the articular surface of the coracoid and with 

 the propterygium. 



The propterygium (prp) is small, subtriangular or oblong, and — 

 articulating in the cavity of the articular surface of the coracoid — fur- 

 nishes a convex facet for the mcsopterygium. It is not fused with the 

 coracoid, as might be understood from the figure. The articulation is 

 similar to that of Heptabrauchias, as figured by Alivart, Fins of Elasmo- 

 branchs, PI. LXXV. fig. 3. 



The radials are in three series, of which those of the outer are small 

 and short, and those of the inner elongate. Of the latter, three or four 

 of the anterior have coalesced in an irregular plate. 



The Cartilages of the Pelvis and Ventrals. 



Plate XI. Figr. 1, Plate XII. 



The pelvis is a broad comparatively thin plate of cartilage about twice 

 as long as wide. On the upper surface it is concave, and has a ridge 

 along each sid^. Below it is convex and has a median ridge which bifur- 

 cates forward. Toward the vent the border is concave ; in front the 

 margin is convex. The anterior twelve radials articulate directly with 

 the side of the pelvis. Several of the foremost of these rays are only 

 partly distinct from each other. 



The peculiar shape of this pelvis suggests an embryonic character of 

 other sharks. In embryos the pelvis is longer than in the adult, in 

 comparison with the transverse measurement. An embryo of Hepta- 

 brauchias before me has it half as long as wide, proportions which 

 are intermediate between those of the adult and an adult Chlamy- 

 doselachus. 



