236 E. I. POCOCK. 



and tliird also as slender pillars with a marginal attachment 

 to the sternum, but the fourth pair has vanished. In some 

 of the genera of this group, e. g. Stasiniopus and Pachy- 

 lomerus, an additional apophysis is found on the dorsal side 

 arising from the crest just behind the second apophysis 

 from the anterior end, and directed inwards. Indications of 

 a similar tendon are also observable behind the next suc- 

 ceeding apophysis, and in Acanthodon similar supple- 

 mentary tendons are observaljle behind the posterior two 

 pairs of apophyses. 



In an innnature specimen of Liphistius I find the four 

 normal dorsal apophj'ses of exceptional thickness, and repre- 

 sentatives of the two supernumerary apophyses that occur 

 in Stasiniopus, well developed. Tlie eutosternite in this 

 specimen, however, perhaps on account of its immaturity, has 

 no ventral apophyses extending to the sternum, although the 

 muscular scars are visible at the sides of this plate. This 

 absence of ventral apophyses is full of interest, on account of 

 its repetition in the Arachnomorphas, with which Liphistius 

 has other features in common (PI. 13, fig. 7). 



On the structure of the eutosternite in the Arachnomor- 

 phous spiders (olim Dipneumones) my observations have not 

 been far extended. A few examples of genera belonging to 

 widely separated families have been examined, however, 

 without the discovery of any very marked differences in the 

 structure of this plate. In all there are four pairs of dorsal 

 apophyses corresponding exactly to those of the Mygalo- 

 morphfe and Liphistius, and in all, except Filistata, an 

 additional pair arising, one on each side, between the normal 

 second and tliird pairs, and directed obliquely inwards and 

 backwards. This represents, no doubt, the muscle, sometimes 

 with a tendinous base, which arises in the same position in 

 some of the Mygaloniorphoc, e. g. Pachylomerus. In many 

 strong-legged species, such as Lycosa, Ctenus, and lOresus, 

 it is noticeable that the dorsal tendons are broad and divided 

 distally into two branches. The extension of this split to the 

 root of the tendon would give rise in each instance to two 



