372 SYSTEMATIC ZOOLOGY 



a variable number of smaller, bandlike plates between, while the 

 head and tail are protected by numerous small plates. Some 

 of the armadillos can roll themselves up into a ball, thus pro- 

 tecting the soft parts on the ventral side of the body. One 

 species extends as far north as Texas, the nine-banded armadillo, 

 which has eight or nine intermediate plates ; it attains a length 

 of seventy-five centimeters. The armadillos are provided with 

 teeth, some having as many as one hundred ; they are nocturnal 

 in habit and carnivorous. While the living species are never 

 very large, we have fossils which attained a length of over three 

 and a half meters and had the shell in a single piece on the 

 back, resembling the carapace of the turtles (Fig. 365). 



Order 2. Sirenia 



The Sirenia (Lat. siren, a siren) are large, aquatic mammals 

 known popularly as the sea cows. They are covered with a 

 thick skin, which is naked in some cases and in others pro- 

 vided with a few scattered hairs. The external nasal openings 

 are near the anterior end of the head, the eyes are small, and 

 external ears are absent; there is no externally differentiated 

 neck. The anterior appendages are finlike and the posterior are 

 absent, while the posterior end of the body is expanded horizon- 

 tally into a flat tail fin. There are two mammary glands on the 

 thorax. The brain is small, the teeth consist of only incis 

 and molars, the testes lie permanently in the abdomen, and the 

 uterus is two-horned. The bones are remarkable for their great 

 density and weight. Though of considerable size, ranging com- 

 monly from three and a half to six meters in length, they arc 

 perfectly harmless animals, living along the shores of tropical 

 oceans and sometimes ascending rivers for some little distance. 

 They feed exclusively on seaweeds and river glasses, and their 

 flesh, especially in the young, is largely eaten by man. The 

 manatees are the sea cows which inhabit the tropical coasts of 

 America and Africa ; the dugongs are found in the Indian 

 Ocean. Formerly there was a northern sea cow found in the 

 North Pacific, very interesting because of the entire absence of 

 teeth ; it was much hunted for food by sailors and was extermi- 

 nated about the middle of the eighteenth century. There are 

 several fossil genera of sea cows. 



