anv. 16. TWO SQUALODONTS FROM MARYLAND—KELLOGG. 43 
e?. Roots of molars united by a thin isthmus for a portion of their length. 
J}. Roots of molars not strongly bifurcated; crowns high. Three to four 
accessory cusps on posterior cutting edge of molars (Germany). 
Pachyodon mirabilis. 
d?, Molars provided with sawlike cutting surfaces on at least one edge. 
e!, Roots of molars divergent but connected at base by a short thin 
isthmus.7? Enamel crowns of molars ornamented with coarse lon- 
gitudinal striae. Anterior and posterior cutting edges of premolars 
indistinctly sawlike. Crowns of premolars slightly compressed and 
incurved; striae coarse at base and disappearing toward apex of 
crown. Incisors with very long, narrow, and fluted crowns. Nasal 
passages situated in advance of nasals, but their posterior margins 
lie in same plane as anterior margins of nasals. Ascending processes 
of the premaxillae extending as far as but hardly beyond posterior 
margins of nasals. Nasals reduced in size. Frontals forming a 
narrow strip across vertex of skull. Width of supraoccipital superi- 
orly less than one-half greatest width of skull across squamosals. 
Decending free plates of basioccipital greatly reduced in extent. 
Vomer overlaps the basisphenoid and apparently extends backward 
to the basioccipital (Germany)................ Arionius servatus. 
Squalodon meyert. 
Squalodon molassicus. 
e?, Roots of molars divergent basally, and not united by a thin isthmus. 
Enamel of crown strongly rugose, characterized by anastomosing 
striae. Anterior edge of molar possesses a sawlike cutting surface 
on basal half of crown. Posterior cutting edge of molar tooth with 
three well-defined accessory cusps (Italy). .Rhytisodon tuberculatus. 
C*. Molars (one or two) with three roots. 
c'. Anterior edges of premolars and some of the molars characterized by saw- 
like cutting surfaces. 
d', Accessory cusps on posterior cutting edges of molars steplike; one of the 
three roots of at least one posterior molar recurved posteriorly to, or 
beyond tip of the middle root (Italy).... T'rirhizodon catulli (Molin). 
(France) Trirhizodon gervaisit. 
d*, Accessory cusps on posterior edges of molars well defined and freely 
projecting; the first four molariform teeth lack well-defined accessory 
cusps on anterior edge; roots long, united by a thin isthmus for a 
short portion of their length (Italy) [Tuscany]... Trirhizodon suessit. 
(Italy) [Venetia] Trirhizodon catulli (Zigno.) 
II. SHort-BeaKED Group. 
Frontals separated from the supraoccipital on the vertex of the skull by the 
parietals.™ 
B?. Crowns of premolars not provided with sawlike cutting surfaces. 
C'. Molars not constricted below enamel crown. Anterior and posterior cutting 
edges of molars serrated by accessory cusps. Molariform teeth have crowns 
ornamented with coarse striae. Anterior teeth are single rooted, with 
coarse striae. Parietals separate the frontals from the supraoccipital by 
a narrow interval on the vertex of the skull. Skull with reduced inter- 
temporal constriction. 
70 Probst, J., Jahreshefte d. Vereins f.vaterl. Naturkunde in Wiirtt., pl. 1, 1885. 
71 Abel, O., Sitzungsber. math.-naturw. Kl. Kais. Akad. der Wissenschaften Wien, vol. 121, pt. 1, 
text fig., p. 61, and pl. 1, 1912. ‘ 
