584 PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. [1885. 



CONTRIBUTIONS TO THE HISTORY OF THE COMMANDER ISL- 

 ANDS. 



No. 5. — Description of a new species of Mesoplodon, M. Stejnegeri, ob- 

 tained BY Dr. Leonard Stejnkger, in Bering Island. 



By FREDERICK W. TRUE. 



(Accompanied by two figures.) 



Among the specimens collected by Dr. Leoubard Stejneger in tlie 

 Commander Islands in 1883 is the cranium of a young Mesoplodon^ 

 which belongs to a species apparently hitherto undescribed. The skull 

 is quite badly water-worn. The tympanic and malar bones are wanting 

 and the pterygoids are very imperfect. The beak a^jparently wants a 

 few millimeters of its original length. 



In his admirable monograph of the genus Mesoplodon, Professor 

 Flower succinctly contrasts the characters of the different species. The 

 characters to which he draws attention concern the basi-rostral groove, 

 the maxillary and premaxillary foramina, and the teeth. The char- 

 acters of the teeth cannot be brought into service in connection with 

 our specimen, since the mandible is unfortunately wanting Following 

 Professor Flower, the known species may be divided into two groups : 

 (1) those in which the basi-rostral groove is absent or slight and the 

 foramina of the premaxillary and maxillary bones are level ; and (2) those 

 in which the groove is deep and the premaxillar}" foramen is behind the 

 maxillary foramen. Between these two groups the Bering Island skull 

 is intermediate, for while the basi-rostral groove is absent, the premax- 

 illary foramen stands behind the maxillary foramen. 



In general proportions the Bering Island skull agrees closely with M. 

 Hectori, as is evident from the following table of comparative measure- 

 ments : 



Measurements. 



Total lenfrth 



Lengt li of beak 



Breadth of beak at base of notches ■- 



Breadth of beak at its middle 



Greatest breadth of premaxillae proxi- 

 mally 



Breadth of anterior nares 



Extremity of beak to hinder margin of ptery- 

 goids in median line 



Greatest height of craninm from vertex to 

 ptervgdids 



Breadth between centers of upper margins 

 of O! liits 



Breadth between zygomatic spurs of squam- 

 osal 



Breadth of occipital condyles 



M. Hectori. From Jblower. 

 (T. Z-S., X,p.424). 



Millimeters. Hundredths. 



567 



320 



135 



37 



117 

 51 



442 



241 



235 



259 

 92 



100.0 



56.4 



23.8 



6.5 



20.6 



8.9 



77.9 



42.5 



41.5 



45.7 

 16.2 



M. Stejnegeri, sp. nov. No. 

 21112. 



Hundredths. Millimeters, 



100.0 



55.8 



21.2 



7.3 



18.6 

 8.8 



42.9 

 44.1 



44.6 

 15.8 



633 

 353 

 134 

 46 



118 

 56 



272 

 279 



282 

 100 



Though the skull figured by Professor Flower {I. c, pi. Ixxi, fig. 4; 

 Ixxii, fig. 4) is somewhat smaller than ours, the two appear to be of 

 about the same age, and comparisons of part with part are therefore 



