6 



The inner border of the haunch is denticulate (ib. p), but in a less degree than in the 

 four preceding pairs : all are subservient to the preparation of the food for the mouth, 

 which is surrounded by these carding bases of the cephaletral limbs. A subulate appen- 

 dage (PI. II A. fig. 4, s, & PI. IV. fig. 1, VII. s) is attached to the inner angle of the 

 distal end of the fourth joint of the sixth limb. The penultimate joint of the same 

 limb, instead of supporting merely the opposing blade of the chela or pincer, has four 

 petal-like appendages {ib. «, t), besides a minute, elongate, slender pincer {ib. ?, «), termi- 

 nating what seems to be the normal continuation of the limb-joints. 



The arrangement of the six pairs of linibs, in relation to the mouth, is shown in 

 PI. II. fig. 2, in a female Limulus polyphemus. It is here seen, as in fig. 1, PI. IV., 

 that these limbs are aggregated in a limited tract of the concave ventral surface of the 

 cephaletron (a), and are so small in proportion as to suggest their inability to perform 

 more than an accessory share in the locomotion of the species. The last alone, or 

 ' maxilliped ' (vii), is modified for such function. 



Behind this pair of limbs are attached a pair of compressed spinigerous oblong plates 

 (PI. II A. fig. 2*5 & IV. fig. 1*), slightly divergent, with the spinous border directed 

 downward or ' ventrad ; ' they recall to mind the pectinate appendages of the thoracetron 

 in Scorjno. In Limulus they close or complete the oral armature posteriorly, form the 

 ' Idvre inferieure ' of Cuvier t, and a corresponding member of the ' trophi,' according 

 to Savigny ; but Latreille preferred to regard them as the haunches or jaw-lobes of the 

 sixth pair of limbs detached^. The haunch-joints, however, are present, though less 

 dentated, in the limb vii. (PI. II A. fig. 5, i) ; but their palpal part (ib. p) is supplied 

 by nervules having origins distinct from those of the main limb-nerves. The appendages 

 in question have also their own distinct pair of nerves (Pis. II A. & IV. fig. 1, n*), 

 arising between the origins of the main nerve of the limb vii. and that of the ganglionic 

 chord, suggestive of a serial homology with the palpal nervules. I am not, however, 

 satisfied with this as a gi'ound for regarding the parts in question as detached limb- 

 palps ; and I, therefore, propose to call them ' chilaria' §. 



The dorsal surface of the cephaletron is moderately accentuated : certain longitudinal 

 tracts are depressed or produced inwardly, to afi'ord advantageous attachments to muscles ; 

 other tracts are elevated to support the eyes, as outlooks, and also bearing defensive 

 spines. 



The ocelli {a 1 in all the figures) are placed one on each side of the anterior elevation 

 of the mid ridge, which is the highest point toward the fore part of the cephaletron, and 

 from which the dorsal surface of that broad semilunar shield slopes rapidly down to 

 the curved digging-edge. The larger compound eyes (a i) are eqvially favourably placed 

 for a lateral outlook, each upon the outer part of an elevation about the middle of the 

 longitudinal lateral ridge, from which the dorsal surface also slopes rapidly to the dig- 

 ging-edge. The almost horizontal tract between the lateral ridges, bisected by the 

 median ridge, is traversed by the two longitudinal depressions, which are rather nearer 



t " La It-vre inferieivre est en aniere de la demiere paire de machoires, et formee de deux lames dentelees." Ta- 

 bleau clementaire de I'Histoire Naturelle des Animaux, p. 452 (8vo, 1797). 

 i Cuvicr's ' Rcgne Animal,' ed. 1828, vol. iv. 

 § Gr. y£i.\af)ioi', a small lip. 



