PKOF. W. H. ELOWER ON THE GENUS MESOPLODON. 433 



pairs of ribs 1 . In the former the first to the seventh inclusive have distinct articular 

 surfaces on the head and the tubercle ; the seventh on the left side is transitional ; the 

 remainder want the neck and head, articulating only by the tubercle to the extremity 

 of the transverse process of the vertebra. 



In M. grayi the first to seventh on both sides have distinct necks, and capitular and 

 tubercular articular surfaces ; the three others, wanting the head and neck, articulate 

 only by the tubercle to the extremity of the transverse process. The general characters 

 of the ribs are, of course, more marked in the older specimen ; but otherwise they agree. 

 The first is very broad and flat ; and in all the angle and a space beyond presents a 

 more or less strongly pronounced flattened surface on the outer side, with prominent 

 posterior edge. This character, scarcely seen in the first, gradually becomes more 

 marked to the last. None of the ribs materially increase in breadth at the lower 

 extremity. 



The sternal ribs in both skeletons, as in all Physeteridse, are not ossified. 



Pectoral Limb. — The scapula is perfectly delphinoid in form, more even than in 

 Berardius, and therefore further removed from Physeter than any other Ziphioid, 

 Hyperoodon being the nearest. The only differences between the two specimens are 

 such as might arise from want of ossification of the suprascapular cartilage, and of the 

 end of the coracoid process in the younger specimen. The humerus, and especially the 

 ulna and radius, present the simple elongated narrow form characteristic of the 

 Ziphioids, and by which they are easily distinguished from the Delphinidae. Allowing 

 for difference of age, there is nothing by which the two individuals can be specifically 

 distinguished. The same can be said of the bones of the maims, as far as the available 

 materials serve for comparison. In M. grayi both are quite complete ; and in M. aus- 

 tralis one hand is nearly so. 



This segment of the limb closely resembles that of Berardius 2 , except that the 

 singular union of scaphoid and lunar, and of cuneiform and unciform bones, noticed 

 in that animal, does not occur. The bones of the first row, the scaphoid, lunar, 

 cuneiform, and pisiform, are all distinct. In the second row the trapezoid and 

 magnum are united into a single bone, as in the skeleton of M. bidens in the Brussels 

 Museum 3 . The first digit has a single slender phalanx ; the second has six, the third 

 the same number, the last being a minute nodule, scarcely larger than a pin's head ; 

 the fourth has three, and the second two phalanges. These are the complete number 

 of the adult skeleton. 



1 Dr. Haast mentions in a letter (dated March 8th, 1876) that one specimen of M. grayi has ten, another 

 eleven pairs of ribs. 



2 Trans. Zool. Soc. vol. viii. pi. 28. fig. 10. 



3 In the specimen at Gothenburg, Malm figures these bones as distinct, he. cit. pi. v. fig. 52. 



3n2 



