art. 16, TWO SQUALODONTS FROM MARYLAND—KELLOGG. 39 
squalodonts, 20 supposed new species were based either upon isolated 
teeth or small fragments of bone with two or three teeth in situ. 
Many of the others are known only from portions of skulls, and no 
complete skeleton has thus far been described. It is only by careful 
deduction that it has been possible for the writer to incorporate many 
of the species in the key. It will be necessary to observe care in 
accepting the relationships indicated in the key since the relegation 
of certain species as allies to others is largely arbitrary and based upon 
the opinion of the writer. No apology, however, is offered for tabu- 
lating the included data as such scattered descriptions retard progess 
in paleontology as in other sciences more than any errors that may 
occur in the present key. 
The writer realizes that the teeth of cetaceans are not especially 
adapted for the formulation of a key but the lack of detailed data 
concerning the skulls and skeletons of most of the described forms 
prevents one from utilizing such features. 
KEY TO THE SHARK-TOOTHED CETACEANS, EXCLUSIVE OF THE ZEUGLODONTIDAE. 
MICROZEUGLODONTIDAE, 
A!, Molars small; antero-posterior diameter of crown more than 10 mm. and less 
than 16 mm. 
B'. Anterior and posterior cutting edges of molariform teeth with accessary cusps 
or tubercles; the serrations are as fully developed on the anterior as on the 
posterior cutting edge. Enamel of crowns of molars lightly sculptured or 
ornamented with striae. 
b!. Three accessory cusps present on posterior cutting edge of posterior lower 
molars. Cheek teeth, apparently, considerably increased above the typi- 
cal number 44; ten, and possibly more, of those in each maxilla are 
serrate, and two-rooted (Italy)..................Neosqualodon assenzae. 
Neosqualodon gastaldii. 
67. Four to five accessory cusps present on posterior cutting edges of posterior 
lower molars (Caucasus)........-.-.----------Microzeuylodon caucasicum . 
SQUALODONTIDAE. 
Brain case telescoped. Molars with anterior or posterior cutting edges serrated by 
accessory cusps or tubercles. Crowns of molars ornamented with rugose enamel. 
B?, Anterior cutting edges of molars and premolars without accessory cusps (80 
far as known). 
b'. Enamel of crowns of molars ornamented with longitudinal striae, very 
coarse around base and finer toward apex. Crowns of premolars compressed 
CGERMANY) 5 2. shes 52 nus ae Henne ech ote bios aie Microcetus ambiguus.®* 
A?, Molars of medium size; antero-posterior diameter of crowns more than 16 mm. 
and less than 30 mm. 
B'. Crowns of premolars ornamented with rugose enamel and provided with 
sawlike cutting surfaces ® on at least one edge (so far as known). 
® Microcetus, new genus for Phoca ambigua Meyer, 1840. The molars of Microcetus are quite unlike 
those of the other forms grouped under the Microzeuglodontidae. Perhaps they should be allocated 
with the Squalodontidae. 
® The sawlike cutting surface referred to in this key should not be confused with the presence of 
accessory cusps, In the absence of accessory cusps, or when but one or two are present, the anterior and 
posterior edges of the cheek teeth of many of the squalodonts are transformed into carinae which are 
notched or toothed. An excellent illustration of this feature will be found on the plate accompanying 
De Zigno’s article in the Memoires del Istituto Veneto di Sci., Lett. ed Arti, Venezia, vol. 20 for 1876. 
The teeth of this particular specimen, apparently, have this feature very strongly developed. 
