OCR Text |
Show 574 MR. M. T. WOODWARD ON [May 5, it; indications of the paraconid and metaconid are just visible as antero- and postero-internal shoulders to the main outwardly inclined cone (protoconid) ; of two former cones the metaconid appears to develop a trifle the earliest, as in m72~ the paraconid is not yet visible ; in neither teeth had the hypoconid yet made its appearance. The order of development is thus shown to be :- 1. Protoconid. 2. Metaconid. 3. Paraconid. 4. Plypoconid. This same order of development is presented by the cusps of dpm. 4. The probable relation of the dentitions is as follows :- (12 3 fl fO 2 3 4 fl 2 3 4 T J 1 2 °. n}1. v) ° 2 3 4 AF J L< 1 2 3' C-<V R 1 0 2 3 4; U'< - LI 2 3 (1 [ 0 2 3 4 (1234 ERICULUS SETOSUS. The dentition of this genus is somewhat specialized, inasmuch as there is a distinct reduction in number of teeth, the 3rd incisor above and below being, in addition to the 1st premolar, completely wanting. In the case of the functional teeth possessed by Ericulus, the replacement is complete and may be represented as follows:- fl 2 0 fl fO 2 3 4 fl 2 3 TJl 2 0. r J 1. p JO 2 3 4 J L< ] 2~0' L ^ 1' ^ 0 2 3 4' M-< ~ ^1 2 0 [l [0234 ^123 In a fcetal specimen examined, 78 mm. long with a head length of 23 mm., a slight differentiation of the dental lamina in the lower jaw was observed between i72 and c^, indicating the last trace of i7~3; but above the reduction is more complete, for although there was a conspicuous gap present between ij_2 and % yet all trace of the dental lamina was lost. The canines develop close to the 2nd premolar, and no indication of the missing 1st premolar was to be found. Examination of the 4th premolar shows that ppm. 4 develops conspicuously in front of dpm. 4, the former being distinctly betwreen dpm. 3 and dpm. 4, but on their hngual side. Only a slight lingual development of the dental lamina was observed in connection with -'-?. m. 1 The upper molars, like those of Centetes, are of trituberculate form, but possess in addition one slight antero-external cingulum |