SQUALODONTID.£E 257 
Choneziphius4—The rostral portions of crania from the Antwerp 
and Sutfolk Crags, on the evidence of which this genus has been 
established, agree with those of JJesoplodon in having the premaxille 
in contact with the intervening bones throughout the length of 
their inner surfaces, and also in showing only a very small portion 
of the vomer on the inferior surface ; they differ, however, in that 
the mesethmoid cartilage remains unossified, whereby a fistular 
vacuity remains. In some species the soldering of the inner 
surfaces of the premaxille is incomplete. The interorbital region 
of the skull is flat ; and there are two pits in the nasal region, of 
which the right is the larger. 
Fumily SQUALODONTID-E. 
Numerous extinct forms, chiefly known by teeth and fragments 
of cramia, may be provisionally placed here, until more of ‘their 
osteological characters shall be brought to light. They differ from 
all existing Cetaceans in having the teeth distinctly differentiated 
into groups, as in the Archzoceti, the posterior molars being two- 
rooted. The cranium has, however, none of the distinguishing 
characteristics of the Zeuglodonts, but essentially resembles that of 
the Odontoceti, especially in the position of the anterior nares and 
form of the nasal bones. 
Syuetlodon?—All the forms may be included in this genus, the 
so-called Lizoprion not being distinct. Dentition: 7 3, ¢ 7, simple 
teeth of the molar series (premolars ?) 4, two-rooted molars #=14 ; 
total 60. The double-rooted molars differ from those of Zenglodon 
in having the denticulations of the crown confined to the posterior 
border, or at all events much less developed on the front edge. 
Very little is known of the structure of these animals beyond the 
skull and teeth, fragments of which have been found widely 
distributed throughout the marine Miocene and early Pliocene 
formations of Europe, especially in the Vienna basin, many parts 
of France, and the Antwerp and Suffolk Crags. They have also 
been found in formations of corresponding age in North America 
and South Australia. A few isolated teeth have been met with in 
the cave-deposits of Italy, which, if contemporancous with the beds 
in which they occur, indicate the survival of the genus into the 
Pleistocene period. 
Family PLATANISTID-£. 
Under this heading may be placed three very singular genera, 
which, though differing considerably from each other, have several 
1 Duvernoy, op. cif. p. 61. 
2 Grateloup, lef. fe. 2. Sef. Bordeana, 1840, p. 208. 
17 
