CRUSTACEA ENTOMOSTRACA. 



operculum, which lies within the aperture of the testa, and when^closed 

 over the retracted thorax by the action of the adductor scutorum muscle 

 forms a protection to the contained soft parts of the animal. 



The remarkable departure from the symmetrical type presented by 

 the Verru <idae is described below. 



The rrn uih opens on a prominent oral cone which projects 

 backwards (Fig. 272, M K}. In front is the large hood-like 

 labrum, and at the sides are situated the toothed mandibles with 

 their palps (Fig. 274), the toothed first maxillae, and the setose 



FIG. 274. Mouth parts of Lepas. A seen from the right. B oral appendages of left side 

 isolated and seen from the inner aspect ; Mn mandible ; Mn. p and p mandibular palp ; 

 Mx l 1st maxilla; MX* 2nd maxilla; u.l. labruin. 



swollen second maxillae which together limit the mouth cavity 

 posteriorly. The six pairs of long, black, ma l ny- jointed, biramous. 

 thoracic appendages (cirri) are curled towards the mouth, and 

 richly beset with setae. With those of the opposite side 

 they form a hand-like structure, which is rhythmically thrust out 

 of the aperture of the mantle and swept through the water with 

 a grasping motion, producing currents and capturing food. 

 The abdomen has almost entirely disappeared, but from the 

 ventral side of it there springs the long probosciform penis. A 

 caudal fork represented by two short lobes is usually present in 

 the Pedunculata and usually absent in the OperculMa. In 

 some genera of the former (Alepas, Ibla and Lithotrya), in the 

 Ascothoracica and some Acrothoracica its lobes are lo.nger 

 and articulated. In Lepas two or more hollow processes situ- 

 ated near the bases of the anterior pair of thoracic feet a.^e 



