INIA GEOFFRENSIS AND PONTOPORIA BLAINVILLII. 113 
I will now endeavour to formularize the distinctive characters of these three primary 
groups of the OpoyToceT!, giving them the rank of families. 
1. Puysererip#, Costal cartilages not ossified. The hinder ribs losing their tuber- 
cular and retaining their capitular articulation with the vertebra. The greater 
number of the cervical vertebrae ankylosed together. Pterygoid bones thick, 
produced backwards, meeting in the middle line, and not involuted to form 
the outer wall of the postpalatine air-sinus. Symphysis of mandible of moderate 
or excessive length. No functional teeth in upper jaw. Mandibular teeth various, 
often much reduced in number. Lachrymal bones usually large and distinct. 
Bones of the skull raised so as to form an elevated prominence or crest behind the 
anterior nares. Orbit of small or moderate size. Pectoral limbs small. Dorsal 
fin usually present. 
II. Praranistip£. Costal cartilages not ossified. The tubercular and capitular articu- 
Ill. 
lations of the ribs blending together posteriorly. Cervical vertebra all free. Ptery- 
goid bones thin, not conforming in their mode of arrangement with either of the 
other sections. Jaws very long and narrow; both with numerous teeth having 
compressed fangs. Symphysis of mandible very long, exceeding half the length of 
the entire ramus. Orbit very small. Lachrymal bones not distinct from the 
jugal. Pectoral limbs large. Dorsal fin rudimentary *. 
DeLpHinip&. Costal cartilages firmly ossified. Posterior ribs losing their capi- 
tular articulation, and only uniting with the transverse processes of the vertebrae 
by the tubercle. Anterior (2-6) cervical, in most, ankylosed together. Ptery- 
goid bones short, thin, involuted to form, with a process of the palatine bone, the 
outer wall of the postpalatine air-sinus. Numerous teeth in both jaws (Monodon 
excepted), sometimes deciduous. Symphysis of mandible short or moderate, never 
exceeding one-third the length of the ramus. Bones of the skull not raised into 
a distinct crest behind the anterior nares. Orbit of moderate size, Lachrymal 
bone not distinct from the jugal. Pectoral limbs varying much in form and size. 
Dorsal fin usually present. 
I. The Physeteride appear to constitute a very natural group}. This may, however, 
be divided into two well-marked subfamilies :— 
that Mr. Darwin has informed me that he met with no evidence of the existence of a freshwater Dolphin in the 
La Plata system of rivers, and that no mention is made by Azara of any such animal. 
* These characters are subject to modification when more is known of the structure of Pontoporia. 
+ Van Beneden insists strongly upon the close affinity of Physeter with the Ziphioids: he says, ‘Comme on. le 
voit, les Cachalots sont pour nous des Ziphioides yéritables, portant une rangée de dents fortes et espacées sur 
chaque branche de maxillaire ” (Mém, sur yne Nouy. Espéce de Ziphius, Mém. de l’Acad. Royale de Belgique, 
t. xvi. 1863), 
R2 
