Mr. A. Tulk on Obisium orthodactylum. 55 



second interstice is in part also raised, and forms an oblong 

 slightly raised hump near the base of the elytron ; this hump 

 being destitute of scales presents a black mark ; again the 

 fifth interstice is strongly convex, excepting for a short distance 

 from the base of the elytron ; the sixth interstice is convex, — 

 strongly so at the base of the elytron, and projects in the form 

 of a rounded angle at the shoulder, but posteriorly the convexity 

 of this interspace decreases; on the hinder half of the elytron 

 it is flat : the convex portions of both the fifth and sixth inter- 

 stices are denuded of scales, and so is the lateral margin of the 

 elytron ; so that as regards the colouring, the elytron may be de- 

 scribed as silvery green, with the suture, a small oblong mark at 

 the base, a semi-lateral mark extending from the base nearly to 

 the apex, and the lateral margin black, if we except a small por- 

 tion of the latter at the base of the elytron. Numerous longish 

 pale hairs are observable on the apical portion of the elytra. 



VIII. — Note upon Obisium orthodactylum [Leach), 

 By Alfred Tulk, M.R.C.S., M.E.S. 



So much yet remains to be learnt concerning the structure and 

 habits of many of the inferior forms of Arachnida, that every ob- 

 servation tending to throw additional light upon them cannot 

 but be regarded by the naturalist as deserving of record. Upon 

 the internal edge of either claw of the chelicerse, in the above- 

 named species of Pseudo-scorpion, we perceive, under the micro- 

 scope, an immoveable pectinated appendage, of a delicate white 

 colour and transparent texture : that upon the external claw, to 

 nearly the middle third of which it is attached by about half the 

 extent of its back, is the most prominent, and consists of fourteen 

 slightly curved and obtuse teeth, which gradually increase in 

 length from behind forwards, the posterior one differing from the 

 rest in its rounded form and greater breadth. The internal, 

 from not being implanted so directly upon the edge of the claw 

 as the preceding, but deeper down towards its base, is less distinct, 

 its extremity alone projecting so as to render visible four or five 

 of its teeth, the remainder of which are with difficulty counted, 

 though a careful examination has at length convinced me that 

 their total number is the same as upon the other comb. The 

 plane of position of the two claws, when the chelicerse are at rest, 

 is obliquely downwards and outwards, so that the internal is 

 placed most superiorly, and overlaps by its apex that of the ex- 

 ternal. The two combs preserve constantly this slanting direction 

 towards each other. But, besides these organs, there arises from 

 the front of a slightly elevated ridge upon the inferior surface of 



