30 



BRITISH FOSSIL CETACEA 



This genus was founded by Duvernoy^ on the head or skull of a Zlph'ms brought 

 from the ' niers de la Nouvelle Zelande ' by M. Arnoux, chirurgien-nuijor of the corvette 

 Le Jiliin, commanded by Capt. Berard, and presented by him to the Museum of Natural 

 History in the Garden of Plants in 1846. The animal is stated to have been stranded 

 at Port Akaroa, Banks' Peninsula, New Zealand. It was about 32 feet in length, 

 and the skull (fig. 11) measured 4 feet. The cranium is rather more symmetrical 

 than usual, and show^s, as in Ziphius indicus, a beginning of the vertical productions 

 of the maxillaries (e) which distinguish, by their full development, the genus 

 Ilyperoodon. 



The premaxillarics (22, 22') are divided along the upper part of the rostrum by a 

 channel (originally occupied by the unossified basis of the prefrontals), exposing 

 the upper groove of the vomer, and giving to the transverse section of the 

 rostrum a deep upper eraargination (" la forme demi-cyhndrique,'' Duvernoy, ib., 

 p. 53). 



The prenasal fossa) (fig. 11, 22') contract forward to the entry of the incisive or naso- 

 premaxillary canals (^), as in Ziphius plajiirostris, Cuv. (fig. 2, rf, d, p. 5). In the non- 

 ossification of the prefrontal cartilage, Ziphius Arnouxii participates with Z. Gervaisii, Z. 

 micropterus, and Z. patachonichus. The anterior (c) of the three outlets («, b, c) of the 

 sub-orbital or antorbital canal opens into a better defined depression of the maxillary (at 

 c, fig. 11) than usual, but this cannot be interpreted as generic. The ecto-maxillary 

 ridges (e) have a rugous exterior,- as in Ziphius Cuvieri (fig. 3, p. 6). The vomer ' puts in 

 an appearance ' at the under surface of the rostrum, between the maxillaries and pre- 

 maxillarics, for an extent of about 1 foot 3 inches. Herein Z. Jmouwii resembles 

 Z. Layardi, but combines the character with a non-ossification of the prefrontal rostral 

 cartilage. The mid-pterygoid keel shows a fiissure due to non -confluence of the descending 

 plates. In all these characters we have specific modifications of an essentially generic 

 ziphial type. The value of the mandibular dental character will be discussed in connection 

 wdth the next nominal genus. 



^Iesodiodon, Duvernoy. — The chief character of this genus is the position of the 

 developed pair of mandibular teeth (figs. 12 and 13).'^ On this character I would remark 

 that more than one pair of teeth or of gingival tooth-germs are formed in the alveolar 



1 'Annales des Sciences Nat.,' 3e s^rie, "Zoologie," torn, xv, pi. i. 



2 Are these the parts defined as intermaxillaries, rather swollen on side of blowers,'" in Gray, 'Catal. 

 of Seals and Whales,' 8vo, 18Gf), p. 327 ? 



3 " III. Le genre Mesodiodon, nob., caracterise par I'existence de deux dents d^veloppes et alveo- 

 laires a la machoire infcrieure, qui sont implantees bien en arri6re de celles du genre precedent, a peu pres 

 nu commencement du second tiers de la longueur de chaque branche raandibulaire. Ce genre, distingue 

 d'aillcurs par d'autres caractures importants, se compose de quatre especes, dont trois vivantes et une 

 fossile." — Duvernoy, loc. cit., p. -11. 



