61 



from the external margin, is, in a very small degree, 

 depressed, and displays a number of broken and con- 

 tinuous strise, parallel to that margin. There are no 

 traces of organs of vision. The buckler is nearly the 

 segment of a circle; anterior edge, in the present 

 case, imperfect; it is four inches and three-fifths 

 broad, and one inch and one-ninth long at the centre; 

 it joins the abdomen by a somewhat sinuous trans- 

 verse line; cheeks and front of equal breadth; the 

 former are flat, but rise at the sharp ridge by which 

 they unite with the front; they are triangular in 

 shape; their outer angles terminating by an acute 

 tip. The striae mentioned above are here not quite 

 parallel to the external border; the front is a shallow 

 depression; rounded but tapering anteriorly; it is in- 

 tersected from above on each side obliquely towards 

 the mesial line, by a ridge bifurcating downwards; 

 another smaller ridge nearly bisects the front perpen- 

 dicularly. 



The abdomen and post abdomen are not distinct. 

 The abdomen exclusive of the cauda is three inches 

 and a half long; it exhibits fourteen costae varying 

 indiscriminately from one-fifth to one-fourth" of an 

 inch in breadth, except the three inferior ones, which 

 are rather broader; they occupy the -whole abdomen 

 without nnembranaceous interspaces, and are sepa- 

 rated by a black sulcus, not always well defined, and 

 sometimes a line in diameter. Each costa is canali- 

 culated from the upper and under angle to the tip. 



The middle lobe is separated from the lateral by a 

 shallow, rude sulcus, which however, does not al- 



