546 MB. W. F. LANCHESTEE ON THE [Dec. 3, 



orbital angles iu the younger individuals, and its margin is a little 

 straighter. 



Oue individual, from Karri pong Pateling, is called, according to 

 the label on it, by the name " Ketam Kertak." " Ketam " is the 

 ordinary word for crab ; I am unable to find a meaning for the 

 word "Kertak" 1 . 



Dim. S 47-5 x 39. J 43 x 34. J 43 x 35. d 33-5 x 28. 

 6 27x23. tf 20-5x13. $40x34. $40x33-5. $ 22-5 x 

 19-5. 



34. Potamon (Paeathelphusa) improvisum 2 , sp. n. (Plate 

 XXXIII. fig. 2.) 



Loc. ? 



One female. 



In this species the carapace is very depressed posteriorly behind 

 the postfrontal ridge, but in front of this ridge it slopes down 

 rather steeply towards the frontal and antero-lateral margins. 

 The actual front, however, is directed nearly horizontally, and 

 presents a faintly concave upper surface ; its anterior margin is 

 rather sharp and its course sinuous, this latter being due to the 

 presence of a broad and shallow notch in the median line, and to 

 the sloping away of its outer angles into the upper orbital borders. 

 The latter are very slightly swollen, noticeably at their internal 

 angles, hardly at all at their external angles, where these run into 

 t he extra-orbital teeth ; a shallow notch is discernible under the 

 lens at the middle of the border. The orbits themselves are deep, 

 their width is a little more than half that of the front, which is, 

 in turn, one-third of the width of the carapace at its widest point 

 (viz., between the last epibranchial teeth). The lower orbital 

 border, seen under the lens, is crenulate, and presents at its inner 

 angle a distinct tubercular tooth with two rounded heads, which 

 are placed so that the one lies above the other in the natural 

 position of the animal, and which are separated by a shallow 

 groove, the said groove being continued downwards and backwards 

 nearly to the anterior buccal angles. 



The antero-lateral borders are about as long as the front is wide, 

 or two-thirds the length of the posterolateral, and are armed with 

 four teeth, including the extra-orbital. Of these teeth the 1st is 

 forwardly directed, triangular, blunt, and broad at the base ; the 

 2nd, separated by a very short rounded interval from the 1st, is 

 the smallest of all, forwardly curved, sharp, and conical ; the 3rd, 

 separated from the 2nd by a slightly greater rounded interval, is 

 closely similar to the latter, but twice as big ; while the 4th, whose 

 tip is as far from that of the preceding tooth as the latter is from 

 the tip of the extra-orbital, is more outwardly directed, its anterior 



1 "Kertak," Mr. Laidlaw informs me, is an orthographical error; the word 

 should have been written " Katak," meaning "a frog." 



2 A similar abbreviated metamorphosis is known for Potamon flttviatilv, 

 Dilocareinus, and Trichodactylus (cf. Ortmann, Eronn's Thierreicli, v. 2, 

 p. 11)98). 



