82 Mr. C. Spence Bate on Diastylis echinatus. 



parallel with the edge of the carapace. A second serrated cor- 

 rugation is situated a little behind the first, one-half of which is 

 subparallel with the dorsal surface ; the other half lies at a right 

 angle to it, and is subparallel with the anterior margin of the 

 carapace, and corresponds somewhat with the direction of the 

 first ridge, but extends to less than half its length. The angle 

 formed by the two lines is surmounted by a strong spine; a 

 similar spine marks the centre of each divergent line. 



Situated still posteriorly is a third serrated ridge. It origi- 

 nates near the centre of the median dorsal line, and appears to 

 repeat the second line, that is, it traverses first a line diagonally 

 produced anteriorly, and then suddenly bends at an angle that 

 is rather less than a right angle; proceeding downwards and 

 backwards, it terminates in a semicircular bend. Lower down 

 (that is, nearer to the lateral margin) this semicircular serrated 

 ridge is twice repeated, the anterior of which, from its position, 

 appears to correspond with the line of the second ridge, of 

 which it may be an imperfect continuation. The third ridge, 

 like the second, has the angle that is made by its change of 

 direction tipped with a strong spine : a similar spine stands near 

 the middle of the upper half; but the lower half is not so marked. 

 A strong spine occupies the centre of the dorsal line at the point 

 where the third ridge meets the one upon the opposite side. 

 Two other somewhat stronger spines occupy the median line 

 posteriorly to the one mentioned, and a third, much smaller, 

 stands upon the extreme limit of the posterior margin of the 

 carapace. Two spines on each side, subequally distant from 

 each other and the central, also stand upon the posterior mar- 

 gin ; and the carapace is armed all over with subequidistantly 

 placed, short, stout spines. 



The eye is situated in a deep notch in the median line corre- 

 sponding with the anterior point of the second serrated ridge. 

 Behind, near the median line, but on each side of it, are two 

 closely placed small spines, and still further back in the median 

 line are two strong spines, subequally distant from each other 

 and from the organ of vision. 



The pereion has four somites exposed behind the carapace, 

 the first of which is narrow, and narrows laterally until it is lost 

 beneath the carapace; it is serrated along the anterior margin, 

 and armed on the dorsal median line with a short strong spine. 

 The second somite is broader than the first, and increases in 

 width towards the lateral extremities. The dorsal median line 

 is crowned by a central spine that is longer than that on the 

 first, and a small lateral spine or tooth that is planted close but 

 slightly anterior to it ; the anterior margin, for about half the 

 extent of the somite, is slightly serrated. 



