ISAENIDiK. 



77 



is a groove. From a point a little behind the center of each vertebral scute a few folds radiate 



to the ends and angles of the scutal areas. Outside of these areas the surface of the shell is 



somewhat uneven. 



The anterior neurals are widest in front, very narrow behind. The three or four posterior 



are wider. The sutures are somewhat irregular. Only / neurals can be determined. The 



seventh is larger than the others and corresponds to the seventh 

 and eighth costal plates; but no suture can be seen crossing it. 



The nuchal bone is slightly broader than long, 46 mm. by 35 

 mm. The pygal, somewhat damaged, is broader than long. 

 The peripherals do not differ greatly in height, this being about 

 2/ mm. There were apparently 12 of these bones on each side. 

 The sulci are distinctly imprest, but narrow. The nuchal 

 scute is distinctly divided into a right and a left. At each side of 

 it is a minute triangular first marginal. The second marginal is 



3J mm. long on the free border; the third, 39 mm.; the eighth, 38 mm. The dimensions of 



the vertebral scutes are shown in the table. 



Figs. 59 AND 60. Ba'ena riparia. Type. Xj. 



59. Carapace, showing bones and scute areas. 



60. Plastron, ab, abdominal scute; an, anal scute; enl, eutroplastron; epi, epiplastron; fern, femoral scute; g, 



gular scute; hum, humeral scute; hyo, hyoplastron; hypo, hypoplastron; infm, inframarginal scutes; 

 mes, mesoplastron; pec, pectoral scute; xiph, xiphiplastron. 



There are on each side 5 costal scutes, a small supernumerary one being situated on each 

 side of the first vertebral. Whether there are 13 or 14 marginals is uncertain. There is no 

 supracaudal scute occupying the midline over the tail. 



The plastron (plate 18; text-fig. 60) is 262 mm. long on the midline. Its width is close to 

 200 mm. As in the other species of the genus, it sends upward strong axillary and inguinal 

 buttresses. The former rise to within 25 mm. of the first dorsal vertebra. They are joined 



