R. I. Pocock — On Eophryniis and Allied Arachnida. 447 



lamina is seen to extend downwards and forwards to the anal 

 plate and to be continuous on each side with the crescentic sternal 

 sclerite of the tenth somite, which encircles the anal plate and is 

 merely separated from the posterior lamina by a shallow groove 

 on each side. 



Here, then, three questions offer themselves for decision : — 

 Does the crescentic sternal plate of the tenth somite belong to 

 the somite of which the anal plate is the tergal representative? 

 Or is the tergal region of the tenth to be found in a part or 

 the whole of the area that lies behind (morphologically above) 

 the anal plate ? And is the posterior median lamina an extension 

 of the tergal region of the tenth or of the ninth somite ? If an 

 affirmative answer be given to the first question, the number of 

 somites of the opisthosoma will be fixed at ten. If the second 

 question be answered in the affirmative, the number in question 

 will be eleven, the anal plate representing the dorsal sclerite of 

 a somite without sternal element. With regard to the third 

 question, the absence of all divisional line on the dorsal side 

 between the tergum of the eighth somite and the posterior median 

 lamina in Eophrynus prestvicii, Kreischeria wiedei, and Anthracomartus 

 volkelianus points to the correctness of Haase's view that the 

 lamina belongs to the last somite visible on the dorsal side. 

 Again, with regard to the second question, Haase's figure of 

 the ventral surface of the posterior end of the opisthosoma of 

 A. vollcelianus, and that of the same region in JSopJiryniis (Brachypyge) 

 carhonis of Howard & Thomas, attest the presence of a distinct 

 annular somite, with sternal, tergal, and lateral regions in front of the 

 anal plate. In Eophrynus prestvicii this same somite is recognizable, 

 although its tergal area, lying behind (morphologically above) the 

 anal plate, is very narrow, much narrower indeed than the corre- 

 sponding area as represented in Anthracomartus volkelianus. This 

 somite in Eophrynus I count as the tenth. The anal plate then 

 represents the eleventh. This plate has the form of a transversely 

 oval tubercle, and in one of the casts is marked by an incomplete 

 transverse groove which suggests the possibility of its consisting 

 of distinct sternal and tergal elements. If this be the case, the anal 

 somite will resemble that of the Amblypygous Pedipalpi, rather 

 than that of the Cyphophthalmous Opiliones. In other respects the 

 segmentation of the posterior end of the opisthosoma closely resembles 

 that of the last-mentioned group (e.g. of Stylocelliis), where the last 

 tergal plate, the eighth, visible on the dorsal side, overlaps the ninth ; 

 the latter forms a narrow ring round the tenth, of which the tergal 

 element alone persists as the anal plate or valve, its sternal equivalent 

 having apparently disappeared. 



I can find only nine sternal plates as compared with the eleven 

 tergal plates. The discrepancy may be accounted for by the dis- 

 appearance of the sterna of the eleventh or anal somite, and of the 

 first, which has probably atrophied in connection with the enlarge- 

 ment and mesiad approximation of the coxge of the last pair of 

 appendages, and is no doubt represented by the narrow area between 



