D TYPE OF THE FOSSIL CETACEAX AGOEOPHIUS PYGM^US 



While it is true that both the rorquals and Agorophius have large and wide 

 temporal fossse and a compressed vertex, these are, I think, only superficial 

 resemblances. In all existing rorquals {Balcenoptera, Megaptera and the aberrant 

 Bhachianectes) the orbital processes of the frontals are pushed backward toward 

 the brain-case, and are scarcely covered at all anteriorly by the maxillae. In 

 Agorojphius the frontals are almost entirely covered by the maxillse and a wide 

 space intervenes between them and the brain-case. In Agorojahius again the 

 median constriction at the vertex is formed by the parietals, while in the 

 rorquals it is formed, superiorly at least, by the frontals, which meet the supra- 

 occipital and exclude the parietals from the top of the skull. 



In the Tertiary rorquals, Heterocetus, Mesocetus, Idiocetus, Aulocetus, etc., 

 in which the parietals appear on the vertex for some distance, the relations of 

 the frontals and maxillse ai'e not substantially different from those found in 

 existing genera, and show no closer approximation, so far as I can see, to the 

 relations of these bones in Agorophius. The ancestor of the rorquals and other 

 whalebone whales was, in my opinion, a very different form from Agorophius, 

 and is quite unknown. 



The association of Agorophius with Squalodon has much to commend it, and 

 suggests itself especially on account of the form of the teeth. That it is, how- 

 ever, a close ally of typical species of Squalodon appears to me improbable. In 

 such forms as S. bariensis, servatus, etc., the cranium exhibits the antero- 

 posterior compression at the middle of the cranium and the overlapping of the 

 maxillary, frontal, and parietal bones in as marked degree as in existing 

 delphinoids, indicating an advanced development in this direction. In Agoro- 

 phius the parietals separate the frontals from the supraoccipital by a wide 

 interval on the superior surface of the skull, and the postero-external border 

 of the frontal is somewhat exposed, impressing on the skull a very different 

 appearance from that of the typical Squalodons. There is one species assigned 

 to Squalodon, however, which presents a much closer resemblance to Agorophius. 

 This is S. ehrlichii Van Beneden.' It is but little larger than Agorophius, or 

 perhaps about equal in size. Like Agorophius, but unlike other species of 

 Squalodon, it has a broad rostrum. The figures of S. ehrlichii published by Van 

 Beneden^ and by Brandt' are very unsatisfactory, indicating that the specimens 

 are very imperfect and in exceedingly poor condition. Most unfortunately of 

 all, the region of the vertex is especially imperfect, so that there is no possi- 



» Mem. Acad. Belg., 35, 1869, p. 72, pis. 2-3. 



' Loc. cit. 



' Mem. Acad. .Sci., St. Petersburg, 20, 1873, pi. 31 ; 21, 1874, pi. 4, flgs. 12-17. 



