107 



Page 44. Diastylis Rathkei, \ar. 



(I'l IAN I, XXII.) 



k*. On page -4.') I li.-i.vc mentioned tli;i1 some forms of I)'ntxtt/Hs 

 ci'/ ditVcr conspicuously from the type described by Kroyer. in tlieir more 

 spiny carapace, and apparently form a transition to the British species I), linuli// 

 Norman. These forms I propose to combine as a distinct variety, of which 

 figures, both habitus and detail, are given in the last .'! plates. It will be seen, 

 on comparing these figures with those given on PI. XXXIII and XXXIV, which 

 are from a typical specimen, that this variety exhibits several .differences, not 

 only in the form and armature of the carapace, but also in the structure of the 

 ^veral appendages. In my opinion, however, these differences are not great 

 enough to warrant a specific distinction, and I therefore do not find it neces- 

 sary to give any exhaustive diagnosis of this form. Meanwhile it may be of 

 interest to call attention to some of the more conspicuous differences from the 

 typical form. Whereas in the latter (see PI. XXXIII) only 3 small spinules 

 are found on each side below the frontal lobe, there is in the present variety a 

 considerable number of such spinules. giving the anterior part of the carapace a 

 rather scabrous appearance (see PI. LXX). These spinules are even partly 

 continued beyond the middle of the carapace along the most prominent part of 

 the branchial regions. The spinules of the frontal lobe have a somewhat vari- 

 able arrangement, being disposed in some specimens (see the 2 habitus-figures) 

 in 2 or 3 transverse rows, whereas in other specimens (see the 2 figures of the 

 carapace) they form 2 longitudinal rows, as in the typical form. As to the 

 shape of the carapace, a rather conspicuous difference is observed in the devel- 

 opment of the subrostral corners, which in the typical form are distinctly pro- 

 minent, whereas in the present variety they are almost obsolete, causing the 

 anterior part of the carapace, when viewed laterally, to appear more conically 

 tapered. The mucroniform processes of the last pedigerous segment in this 

 variety always point straight behind, whereas in the typical form, they are 

 slightly divergent. In the structure ol the appendages the following differences 

 may be noted. On the superior antenna;- I have failed to detect any trace of 

 the strong denticle found in the typical form at the end of the 1st peduncular 

 joint. The 1st pair of legs appear somewhat more slender, with the outer joints 

 more elongated, and this is also the case with the 2nd pair, the last joint of 

 which in particular is conspicuously longer than in the typical form. The telson 

 considerably exceeds in length the stem of the uropoda, and its lateral spinules 

 are more slender and fewer in number than in the typical form. The outer 



