6o 



THE QUARTERLY REVIEW OF BIOLOGY 



and abbreviated posteriorly. The rela- 

 tions of the bones on the ventral surface 

 of the skull are quite different from con- 

 ditions in the iniids. 



Squalodelphis differs from Diochotichusin 

 the following particulars : antorbital max- 

 illary protuberance slightly more accentu- 

 ated; rostrum narrower at base; maxil- 

 lary almost wholly concealed at base of 

 rostrum by overlying premaxillary; 15 

 teeth in each maxillary and mandible; 

 posterior teeth unicuspid, compressed, 

 bicarinate, and acuminate, and covered 

 with rugose enamel with a cingulum 

 formed by rugosities on internal side at 

 base; length of skull about Z5 inches; 

 symphysis one half total length of 

 mandible. 



A distinctly modernized ziphioid, 

 M-io-ziphius belgicus (Abel, 1905), which is 

 not so distantly related to living beaked 

 whales, was a member of the Upper Mio- 

 cene pelagic fauna of the Belgian coast. 

 Its skull is slightly larger than that of the 

 living Mesoplodon. It is rather ponderous 

 and slightly asymmetrical. It has the 

 thick extremities of the premaxillary 

 bones bent upward opposite the nasal 

 bones; the olfactory foramina are open 

 even in old individuals; large prenarial 

 fossa; no mesorostral ossification; maxil- 

 laries strongly swollen in front of antorbi- 

 tal notches; premaxillaries in contact on 

 distal half of rostrum, completely conceal- 

 ing vomerine trough; maxillary with 37 

 to 48 closely approximated alveoli, but 

 with intervening septa almost entirely 

 obliterated, giving rise to a broad shallow 

 alveolar gutter. The mandibles have a 

 short symphysis, about one-fourth the 

 length of the rostrum, and are furnished 

 with two pairs of large functional teeth, 

 of which the anterior or terminal pair is 

 the larger. These teeth are lodged in 

 projecting sockets formed of cancellous 

 bony tissue. The mandibular dentary 



groove is narrow, shallow, and reduced 

 posteriorly. With the exception of the 

 two pairs of mandibular teeth, the others, 

 if present, were lodged in the gum. 



The ziphioid genera Mioziphius, Chonezi- 

 phius, and Ziphius are a direct outcome of 

 a peculiar arrangement of the bones that 

 enter into the composition of the vertex 

 of the cranium. We have seen that the 

 vertex was somewhat raised in the Lower 

 Miocene genera Diochotkhus and Squalo- 

 delphis, and that the premaxillaries were 

 blocked off posteriorly by the raised crest- 

 like postero-internal margins of the 

 maxillaries. Any additional backward 

 thrust of the maxillaries and premaxil- 

 laries would elevate the posterior extremi- 

 ties of these bones, for the maxillaries 

 were in contact with the crest of the 

 supraoccipital in these Lower Miocene 

 ziphioids. Partly in this manner and 

 partly by actual bony outgrowths, the 

 skulls of these Upper Miocene ziphioids 

 acquired their peculiar elevated vertex 

 overhanging a large bowl-shaped postros- 

 tral depression. 



The skull of Choneziphzm planirostris 

 (Cuvier, 1836; Capellini, 1885; Weber, 

 1917) is somewhat unusual in that it is 

 the only Upper Miocene ziphioid known 

 to have a premaxillary that retains dis- 

 tinct vestiges of alveoli, notwithstanding 

 the probability that if teeth were present 

 in the upper jaw they were lodged in the 

 gum. This extinct ziphioid, or closely 

 related species, occurs in the Upper 

 Miocene sands of the Antwerp Basin, the 

 Edisto marl of South Carolina, the 

 Pliocene Red Crag of Suffolk, England, 

 and the Pliocene sands near Siena, Italy. 

 This ziphioid skull is distinguished by 

 having an attenuated rostrum not notice- 

 ably widened at the base, but somewhat 

 swollen and thickened near the middle; 

 form of rostrum subject to age, individual, 

 and perhaps sexual variations; prenarial 



