CHAPTER IV: THE MUSK OR MUD TURTLES 

 FAMILY CINOSTERNID^E 



The Genera AROMOCHELYS andCINOSTERNUM, Composed 

 of Small and Thoroughly Aquatic Species, the Majority In- 

 habiting North America 



ALL of the species of the small family Cinosternida, bear 

 a general resemblance to one another. They are of small size 

 few attaining a length of five inches. The upper shell is bluntly 

 oval in outline, rounded above, and possesses no trace of the 

 flaring edge, or scolloped border as does the shell of typical 

 pond and river turtles. It might be said that the carapace of 

 these turtles looks like a smooth, flat stone. The under shell 

 plastron is a distinguishing character. It is composed of a 

 broad, rigid bridge, and two hinged, movable lobes, that may 

 be drawn up against the carapace slightly so with Aromochelys, 

 but to such an extent with Cinosternum, that the species of the 

 latter genus have sometimes been called "box turtles," an ap- 

 pellation which rightly belongs, however, to a genus of strictly 

 terrestrial turtles (Cistudo)* 



Classification and Distribution. But two genera constitute 

 this family. Aromochelys appears to be represented by three 

 species, all of which occur in eastern North America. The 

 larger genus, Cinosternum, comprises about eleven species, six 

 of which inhabit the United States and northern Mexico; one 

 occurs in Mexico generally except the northern portion, three 

 in Central America, and one in northern Brazil and the Guianas. 

 The structural differences of these species are but slight, and in 

 technical nomenclature described principally from the shape 

 of the shields forming the plastron. The greater number of the 

 species of both genera display much the same colouration of the 

 upper and lower shells. Some slight characters are exhibited 



* With Cistudo, there is no rigid bridge. ^ The plastron is attached to 

 the upper shell by a cartilaginous joint. It is divided by a central hinge 

 front and rear portions closing tightly against the carapace. 



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