116 Cephalothorax in Ricinulei 



2. The Cephalothorax. 



The two principal divisions of the body are, as in Pedipalpi, connected by means of a 

 peduncle formed by the fore-end of the abdomen, and as in Uropygi it is rather broad. 

 They are besides coupled together by a mechanism which is quite peculiar to Ricinulei, and 

 which depends essentially on special adaptation of the anterior extremity of the abdomen. 

 We shall describe this more in detail, when we have treated of the cephalothorax and the 

 abdomen separately. 



The cephalothorax is rather clumsy in shape, being of about equal length and breadth, 

 though the species differ somewhat in this respect. The dorsal surface of the cephalothorax 

 is more or less convex. Its broadest part is just behind the middle, in which place it shows 

 a rounded lateral angle (our " angulus submedius ") placed a little behind the space between 

 the second and the third pair of coxae. From this point forwards the cephalothorax is some- 

 what narrowed, more so in CryptoceUus than in Cryptostemma. 



Cucullus. — Anteriorly the cephalothorax terminates in a large, transversally elliptic, very 

 moveable plate, which articulates with the cejahalothorax and then deflected covers the 

 antennae, the oral orifice and the dorsal surface of the mandibles. Its posterior margin forms 

 a short transversal ridge ; the (upper) anterior surface is convex with a double curvature, 

 and shows in several species a couple of longitudinal grooves. Thorell has already pointed 

 out that the under surface of this plate is concave, and divided into two portions, into which 

 the basal joint of the antenna on either side fits. The ridge which separates these portions 

 is rather high in Cryptocellus Simonis, low in Cryptostemma crussipalpe (PL VII., fig. 1 e), 

 and very low in C. Afzelii. On the outer side each of these concave portions is bordered 

 by a high longitudinal ridge, which starts from the posterior corner of the cucullus, and to 

 the base of which the powerful muscles are attached by which the cucullus is moved, as 

 shown by Thorell {h, p. 11). Along the anterior margin of the concave surface there is a row 

 of rather long and delicate hairs, which are not plumose. 



We have adopted the name given by Thorell to this j)iece, which was described by 

 Westwood as labrum, and by Karsch as clypeus, both of which names are equally misleading. 

 Guerin-Meneville and Gervais compared it to the plate which projects above the antennae 

 and the parts of the mouth in Trogultis, and were thereby led to place Cryptostemma near 

 that genus in the order of Opiliones. The justice of this comparison — though not of the 

 conclusion which those authors founded upon it — is in our opinion more clearly evidenced 

 bj' the fact to which we would here draw attention, that a structure corresponding morpho- 

 logically to the cucullus in Cryptostemmatoidae exists in Thelyphonoidw. In this group we 

 find that a portion of the basal joint of the antennae is covered in a similar manner as in 

 Cryptostemmatoida3 by the projecting anterior part of the cephalothorax, and it is on this part 

 that the central pair of eyes are placed, whilst on its under surface there are two excavations 

 corresponding to the basal joints of the antennae. In short we look upon the cucullus as 

 the first segment of the cephalothorax which carries the eyes — the procephalic lobe of 

 embryologists. The truth of this view cannot be demonstrated in a decisive manner, because 

 none of the Cryptostemmatoidae as yet known possesses eyes; but considering that the cucullus 

 articulates with the cephalothorax, and that the part of the latter which projects in a similar 

 way in Thelyphonoidse carries the front eyes, we have no doubt as to the proper interpretation 



