570 MR. M. r. wooDWAEL ON [May 5, 



Cusps. 



The molar teeth of the adult belong to the trituberculo-sectorial 

 type, the upper ones have square crowns bearing four cusps, i. e. 

 3 large equal ones belonging to the trigon and a small postero- 

 internal cusp or hypocone. The lower molars are elongated, con- 

 sisting of a trigon and a very large heel with two conspicuous 

 cones (hypo- and entoconid) ; the cones in the lower trigon are 

 not equally developed, the protoconid being much larger than the 

 other two. 



My specimen was too young to determine with any certainty 

 the ontogeny of the coues, as only one of the main cones had 

 made its appearance, the dental germ presenting the appearance 

 of a high cone with a large posterior heel (metaconal region) aud 

 a slight internal extension. A plan of the dental germ at this 

 stage shows that structure to be roughly triangular, the main and 

 only cone being situated at the anterior extremity and slightly 

 nearer the external border. From the position of this cone and 

 from a comparison with the cusp ontogeny as seen in the molar 

 of Talpa, with Mhich it is identical in pattern, I think one may 

 conclude that this single cusp is the paracone, the posterior 

 extension representing the metacone, while the internal shelf 

 indicates the position of the future proto- and hypocone. 



In the lower jaw the main cusp is antero-external in position, 

 and may be identified as the protoconid ; a slight inward cxteiision 

 of the dental germ alone indicates the para- and metaconid, while 

 a faint backward development foreshadows the future heel with its 

 two cones. 



The probable order of cusp-development is thus shown : — 



1. Paracone. 1. Protoconid. 



2. Metacone. g f Paraconid. 



3. Protocone. ' | Metaconid. 

 , TT of Entoconid. 



4. Hypocone. 3. j Hypoconid. 



A general examination of the Shrew's teeth shows that with 

 the exception of A, and the almost undifferentiated 1st premolar, 



all the anterior teeth, viz. -'o'/.'.A ' ,< , exhibit the 



- 1. z (i. o) pm. V 



labially situated enamel-germ of a predecessor, some of these being 

 in a highly developed condition, possessing marked dentinal germs 

 but no calcifioatiou. These structures, from a comparison with 

 the teeth of other Insectivora, must be regarded as vestiges of 

 that earlier developed set of teeth the milk-dentition : this homo- 

 logy is very striking when they are compared with the reduced 

 milk-teeth seen in EHnaceus, and is rendered still more certain 

 when we remember that there is indication of no other tooth 

 replacement in the Soriciclcv. 



The relations of t^ are very confusing, for the large develop- 



