The Orders of Mammals Volume 27 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 edition. Excerpt: ...THE LEPTICTID&, ERINACEID&, DIMYLID&. The most primitive representatives of this group are the Eocene and Oligocene Leptictidse. They have already lost one upper and one lower incisor, except Ictops acutidens, which retains three small lower incisors (Matthew, 1903, p. 207, fig. 5); but in the form of the cheek teeth they are much more primitive than the Erinaceidse and some of them retain the minute pmj, which are lost in most Insectivores. The molars in Palceictops and 'Ictops suggest those of the Jurassic Dryolestes in their antero-posterior narrowness, and sometimes (e. g., in the very small Ictops thomsoni Matthew, 1903.1) also in the large size and centro-external position of the paracone. But in the larger species Ictops major (Douglass, 1906, pl. xxii) the molars are much broader antero-posteriorly and the para-and metacones are sub-equal. In all Leptictids p are molariform. The lower molars are tuberculo-sectorial with reduced paraconids and large hypoconids. In crown view the inner and outer cusps are rather widely separated. The replacement of the teeth takes place only after the animal has attained full adult dimensions (Matthew, 1909, p. 534). This delayed replacement is also characteristic, of certain Zalambdodonts and may be a primitive Insectivore character. In Proterix Matthew (1903.2), a primitive member of the Erinaceidw which shows clear evidence of derivation from the Leptictidse, the molars are broader antero-posteriorly and the hypocone is well developed. The molars are in fact described a, s definitely Erinaceid, only the last molar remaining tritubercular, as it does in Hylomys, Neurogymnurus, and Galeri.r. In the living Erinaceidse the antero-posterior broadening of the molars is still more emphasized and they are more...