102 PROCEEDINGS OF THE ACADEMY OP [1819. 



breadth 13 ram., and the height 5 mm.; the jaw alone had behind 

 the articulation (fig. 7a) a breadth of 5.5 to 7.0 mm. in the hinder 

 part; 1 the length of the (free part of the) proc. masticatorius 

 (fig. *lb) 1.5 mm.; the articulation rather prominent in front; the 

 cutting edge in the posterior part slightly undulated, but plain, 

 under the microscope covered with many irregular series of 

 irregular prismatic bodies (fig. 1G) about 02 mm. high. The 

 tougue is large, broad, and high ; the radula narrower than in Tr. 

 ITombergi, brownish-yellow, with nineteen series of teeth. 2 On 

 the under side of the tongue, moreover, the marks of eight series 

 of teeth remain, the teetli themselves having been dropped. There 

 were under the tectum radulse and in the sheath twentj'-five fully 

 developed series, and six which were yet only partly colored. 

 The number of series in all fifty. The number of teeth was, in 

 one of the foremost series of the radula, about two hundred and 

 twenty-five (on each side), and the number seemed not to inci'ease 

 notably farther backwards. The median tooth is like a compressed 

 pyramid, somewhat narrower in the hinder part (PI. IV. fig. 8aa; 

 PI. V. figs, laa, 2a), with the upper part bent backwards (fig. 8); 

 the posterior margin more or less rounded, the anterior margin 

 (fig. laa) with a slight cleft, the continuation of which (fig. 2a) 

 forms a groove on the anterior side of the pyramid. The first 

 lateral tooth shaped nearly as the medial is, but (fig. Sbbcc, 166, 

 2) narrower and longer, the (fig. 8) upper part less prominent, 

 less crooked, and commonly more rounded at the top (fig. 8). 

 The second lateral tooth either nearly like the first (fig. 8a 7 ), or 

 with a distinct beginning of the form (fig. le, 2), that reigns 

 through the long series of external teeth (fig. 12) ; all these lateral 

 teeth are high (fig. 9), compressed, crooked ; the point rather 

 blunt; the basal part of the teeth is continued in an uncolored 



1 The form of the mandibular is rather similar to the figure of Pallas (1. 

 c. fig. 22a). 



2 In a very large individual of the Tr. Hombergi the (always large) 

 radula contained forty-three series of teeth, behind which were forty-seven 

 additional series, the total number of rows being ninety. In the forty- 

 second row or series, on each side, were about two hundred and eleven 

 teeth, in the fifty-second row two hundred and twenty -nine lateral teeth. 

 According to Alder and Hancock (1. c. part vii. pi. 46, suppl.) the number 

 of rows is eighty -four, and the number of lateral teeth two hundred and 

 twenty-one. 



