666 DESCRIPTION OF PLATES, 26, 27. 



to the basal margin ; (s), upper row of shorter bristles ; 

 (t), row of very short bristles, arising from the further side 

 and curling over the crest of the labrum. 

 Fig. 7, Balanus amaryllis : maxilla on twice the scale of the mandible 

 and palpus; (6), upper free segment; (&'), apodcme ; 

 (u 1 ), thickened portion of membrane, perhaps answering 

 to the second segment of the mandibles; (6 2 ), thin mem- 

 brane, extending down to the basal edge of the mouth, 

 possibly answering to the basal segment of the mandibles ; 

 or perhaps the thickened membrane forming the pro- 

 tuberance c 2 in fig. 3, may be considered as the basal 

 segment of the maxillae. 



(u), step-formed projection at lower angle of maxilla. 

 8, Thorax of Coronula diadema : outer membrane of the five pos- 

 terior segments laid almost flat, and viewed externally as a 

 transparent object. 



( 2 ) to ( 6 ), the second to the sixth cirrus, cut off a little above 

 their basal articulations. 



(a), basal curved end of the probosciformed penis. 



(b), anus; (b') } the membrane surrounding the anus, probably 

 consisting of a rudiment of the abdomen. 



(c), rectum, seen through on the under side. 



(d), basal articulation of the sixth cirrus ; (d'), do. of the fifth 

 cirrus; (d 2 ), do. of the second cirrus. 



(e) (<?'), posterior thoracic segment, carrying the sixth pair of 



cirri ; the dorso-lateral portion (e) is separated, in this one 

 segment, from the corresponding portion (e') by a narrow 

 slip of thinner membrane, which may be a part of the 

 abdomen let in. 

 (e 2 ) (e 2 ), thoracic segment, supporting the second pair of cirri. 



(f) (/ 3 ), folds or articulations between the adjoining segments. 

 (ff), swollen, punctured portions of membrane, not differing 



homologically from the rest of the segments. 

 (A), posterior portion of the prosoma, or the specially enlarged 

 part of the thorax ; it carries the first pair of cirri ; homo- 

 logically (h) forms part of the second segment of the 

 thorax of the archetype Crustacean. 



PLATE 27. 

 Nervous System and Senses. 



Fig. 1, Nervous system of Coronula diadema, seen from the ventral 

 surface. 



a, infra-cesophageal ganglion ; two pairs of rather small nerves, 



arising from the dorsal surface, cannot be here shown . 



b, supra- oesophageal ganglion, double. 



c, ophthalmic ganglion, single. 

 D D, eyes, as believed to exist. 



a, three pairs of nerves, running to the gnathites and olfac- 

 tory pouches ; a/ nerve rising from the collar, running 

 towards the mandibles. 



