156 Mr. A. Tulk on the Anatomy o/Phalangium Opilio. 



tour^ elliptical, more or less convex upon its upper surface, ha- 

 ving the lateral margins sinuated and prolonged backwards, the 

 anterior deeply excavated by a crescentic notch, which is inter- 

 rupted in the middle by a slight rounded projection, while be- 

 hind, a transverse curved and elevated ridge (r) supporting a single 

 row of spines marks out its limits from the abdomen. Situated 

 nearly in the centre of the thoracic shield is a large and promi- 

 nent tubercle (/), some^^•hat quadi'ilatcral in form, with the angles 

 rounded off, its transverse diameter being greater than its longi- 

 tudinal, and encroached upon on either side, in an oblique di- 

 rection upwards and inwards, by the round and glistening corneas 

 of the middle pair of eyes. Along the superior and posterior 

 margins of these cornese, but at a little distance from the latter, is 

 a row of obtuse tubercular eminences, and between these a slight 

 groove, dividing the upper surface of the binocular support along 

 the median line. Upon either side, and in front of the latter, the 

 thoracic plate presents a wedge-shaped elevation {e) which extends 

 from the posterior ridge, narrowdng towards the anterior margin 

 of the thorax, beyond which it projects. Its anterior angles are 

 furnished with a cluster of tubercles, and towards the plane of 

 position of the ocular support it inclines downwards, so as to leave 

 a slight circumjacent groove. Upon either side of the thorax, at 

 a point opposite to the interval betwixt the coxsc of the two 

 anterior pairs of legs, is an oblong, laterally compressed ridge, 

 l)ounded internally by an impressed and wavy line, externally by 

 one of the sinuosities of the lateral margins, and which supports 

 a single ovoid cornea (c), having one or more tubercles near to 

 either extremity. From the centre of the anterior margin of the 

 thoracic plate there is prolonged, in a vertical direction down- 

 w^ards, a horny partition (PI. III. fig. 3. s), which separates the 

 cavities for the insertion of the chelicerse upon either side, and 

 which is attached below to wiiat appears, when viewed in situ, as 

 a cordate horizontal body [ex] supporting in front a lanceolate 

 deflexed structure, both of which assist in closing the cavity of 

 the mouth anteriorly, and will be considered, therefore, more in 

 detail in speaking of the manducatory organs. 



The first articulated pieces, commencing from before backwards, 

 which ^^dll require our attention, are the two chelicerce or antenna! 

 claws (PI. III. fig. 3. cli). These organs consist each of two coria- 

 ceous joints. The basal, shorter than the one succeeding and late- 

 rally compressed, has its upper surface convex anteriorly, the lower 

 concave, and prolonged further backwards to form with the pos- 

 terior margin an acute angle, and is received into the cavity, si- 

 tuated with its fellow, upon either side of the vertical septum, 

 above mentioned. These cavities lie immediately beneath the 

 anterior border of the thoracic plate, by inflections of wiiich they 



