i4 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
Toxodontophanus Moreno ; Patagonia resto de un antiguo continente hoy 
submerjido, p. 23, 1882 {nomen nudum)', Ameghino, Observaciones 
generales, etc., p. 64, 1887. 
Patriarchus Amegh.; Contrib. al conoc. de los Mam. Fos. de la Repub. 
Argentina, pp. 480-481, 1889. 
Of all the Santa Cruz Typotheria, Protypotherium is the least specialized 
in dentition and foot-structure, probably approaching more closely than 
any of the other genera the ancestral form from which the group as a 
whole originated. 
Dentition (Pis. Ill, figs. 1, 3, 5, 6 ; IV, fig. 15; V, figs. 11-i^a, 21, 
22). — The dentition is complete and in close series in both jaws. The 
median upper incisors have broad, antero-posteriorly compressed, strongly 
curved crowns, covered externally with enamel, producing chisel-like cut- 
ting edges when worn. These teeth do not grow persistently, but have 
tapering roots. Externally, the crown is convex transversely, with a faint 
suggestion of a broad median groove on the anterior face. Internally, it 
is rendered concave by another broad groove. The second and third 
incisors are of about the same size. The unworn crowns are pointed, the 
point lying at the intersection of a prominent enamel ridge on the 
anterior face with the cutting edge of the tooth. The inner surface of the 
crown is flat in unworn teeth, but in worn specimens develops a median 
groove. The canine is incisiform and indistinguishable from the teeth 
in front. The incisors and the canine are inserted obliquely and im- 
bricate, the posterior border of each overlapping externally the tooth 
next succeeding. The canine is lodged entirely in the maxillary. The 
premolars increase in size posteriorly, but none become completely 
molariform and all grow from persistent pulps. The first is approxi- 
mately cylindrical in section, with a prominent ridge on the external face 
of the crown, which decreases in elevation toward the alveolar border 
and finally disappears, so that in the worn specimens the first pre- 
molar is a simple curved 'cylinder. A slight anterior ridge is observ- 
able in little-worn teeth corresponding to the first of the two external 
ridges in the remaining premolars. Internally the crown, if well worn, 
is convex antero-posteriorly, but in less worn teeth a shallow ante- 
rior groove is discernible. The second, third and fourth premolars 
may be described together. Each has a deep antero-external groove 
bounded by two ridges. In all the species represented in the collections 
