PEOF. W. H. FLOWBB ON THE GENUS MESOPLODON. 431 



Articular surfaces of the arch, or zygapophyses, are developed in all the anterior 

 vertebrEe as far as to between the sixth and seventh in M. australis, and as far as the 

 tenth (though in a very rudimentary condition) in M. grayi. Metapophyses first 

 appear as distinct tubercles in both on the anterior edge of the transverse process of the 

 third vertebra, and gradually increase in size in passing backvpards. Articular sur- 

 faces for the heads of the ribs on the hinder edge of the body occur from the first to 

 the seventh inclusive in both, for the tubercles of the ribs on the transverse processes 

 from the first to the seventh in M. grayi, and to the seventh on the left side only in 

 M. australis. The last tvFO (or the ninth and tenth in M. grayi, and the eighth and 

 ninth in M. australis) have the rib attached to the end of the transverse process 

 springing from the side of the body of the vertebra. The eighth rib in M. grayi is 

 attached to the articular surfaces on the contiguous sides of the body of the seventh 

 and eighth vertebrae, on a line with the last, and not to any transverse process ; so in 

 this specimen seven ribs are attached in the ordinary way by upper and lower attach- 

 ments to body and transverse process, and three to the lower attachment only. In 

 M. australis six were attached by the former method, two by the latter, and the inter- 

 mediate one by the former method on the left, and the latter on the right side ; so that 

 the seventh vertebra and pair of ribs appear clearly to represent both seventh and 

 eighth of the other specimen combined in one, and so to account for the smaller 

 number altogether. 



The lumbar vertebrte are all very much alike in both skeletons. Their bodies, as in 

 all the Ziphioids, are long compared with those of the true Dolphins, their length con- 

 siderably exceeding their transverse diameter. They are strongly carinate below. The 

 transverse processes are short, their length not exceeding the width of the body ; their 

 bases arise from rather more than the anterior half of the sides of the body ; they are 

 all directed forwards, and rounded at the free extremity. The spines are very long, 

 and nearly vertical, much compressed laterally, but broad from before backwards (ex- 

 ceeding half the length of the body), expanding and truncated at their upper extremity. 

 They all have broad, flattened, lamelliform metapophyses, projecting forwards from the 

 anterior edge of the lamina, at nearly the same level throughout the series. 



The caudal vertebrae in the two skeletons bear the closest resemblance in all essen- 

 tial features. The one which I have reckoned as the first of this series difiiers from the 

 lumbar vertebrae in having the keel rudimentary and divided posteriorly, where it 

 presents slight indications of the presence of chevron bones, probably in a rudimentary 

 condition, as they were not preserved in either skeleton. In the second and succeeding 

 vertebrse the median line of the inferior surface is channelled, and has a pair of lateral 

 longitudinal ridges terminating in front and behind in the articular surfaces for the 

 chevron bones. In both skeletons there are eleven of the series of compressed or 

 chevron-bone-bearing caudal vertebrse ; the twelfth is the transitional vertebra ; and 

 there are thirteen of the depressed form, which lie within the laterally expanded portion 



VOL. X.' — rj\KT ]x. No. 4. — August 1st, 1878. Zs 



