1910.] The Sirenia. 407 



Halitherinm was monographed by Lepsius in 1881. (2) Prora.sfomus 

 Owen 1855 from the Eocene of Jamaica, a primitive Sirenian with the 

 complete Eiitherian dental formula. (3) Eotherium Owen (non Leidy) 

 1875 from the Upper Eocene of Cairo Egypt, described more fully by Abel 

 (1904) and by Andrews (190(3). This genus retained a well develo])ed 

 pelvis and femur and together with Eosiren Andrews from the neishborino- 

 FayAm enabled Andrews in 1906 to state new evidence (see below) in 

 support of the theory that the Sirenia are related to the Proboscidea. 



Genetic relations. 



The theory of the relationship of the Sirenia and Proboscidea which was 

 held by de Blainville has been strengthened by the discoveries of Andrews 

 and Beadnell in the Upper Eocene of Egypt. Several remarkable points 

 of resemblance in the soft anatomy of recent Elephants and Sirenians are 

 cited by Dr. Andrews (190G, p. xxi) in the following words: 



" (1) pectoral mammae, (2) abdominal testes, (3) a bifid apex of the heart, (4) 

 bilophodont molars with a tendency to the formation of an additional lobe from the 

 posterior part of the ciiiguUun. [5] The peculiar mode of displacement of the teeth 

 from behind forwards in some members of both groups may perhaps indicate a 

 relationship, although in the case of the Sirenia the replacement takes place by means 

 of a succession of similar molars, while in the Proboscidea the molars remain the 

 same numerically, but increase greatly in size and number of transverse ridges. 

 [6] Dr. Chalmers Mitchell has lately shown (Trans. Zool. Soc, Vol. XVII, 1905, pp. 

 464-7) that the Sirenia and Proboscidea resemble one another in the arrangement of 

 the intestinal tract and that in neither group is there any trace of the Ungulate 

 specialization: it is also significant that he states that //;/raa; likewise approaches 

 the Sirenia in this respect. In a former paper (Phil. Trans., Vol. 196B (1903), 

 p. 116) it was stated that the possession of a non-deciduate zonary placenta was 

 common to the two groups in question, but it has been pointed out by Messrs. 

 Assheton and Stevens (Quart. Journ. Micr. Sci., Vol. XLIX, 1905, p. 1) that this is 

 an error, and that as a matter of fact in the Proboscidea the placenta is deciduate. 

 At the saine time, these writers show that in laoth groups the placenta, in addition 

 to the short villi, also posses.ses a number of larger and longer villi, which deeply 

 penetrate the maternal tissue and seem to be torn off at parturition. Although these 

 points of similarity, taken separately, may be of no great value, together they supply 

 a very strong argument in favor of the close relationship of the two orders." 



In his description of Moeritheriiim and Eosiren Dr. Andrews cites much 

 further evidence for the unity of origin of the two orders. For example, in 

 speaking of the brain of Eosiren (1906, p. 202) he says: "The chief interest 

 of the brain .... lies in its remarkable similarity with that of Mceritherium .... 

 In both animals the hemispheres are divided in a quite similar way by the 

 pseudosylvian depression and the cerebellum is relatively small. In Mcerithe- 



