464 PROF. OWEN ON THE ANATOMY 
extended haunch (48.1). 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 appendage (Pl. XXXVII. fig. 4, s, & Pl. XXXVIII. fig. 1, vir. 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 (40. 6, 7), besides a minute, elongate, 
slender pincer (ib. 7, u), terminating what seems to be the normal continuation of the 
limb-joints. | 
The arrangement of the six pairs of limbs, in relation to the mouth, is shown in 
Pl. XXXVII. fig. 2, in a female Limulus polyphemus. It is here seen, as in fig. 1, 
Pl. XXXVIIT,, 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 ? (vit), is modified for such function. 
Behind this pair of limbs are attached a pair of compressed spinigerous oblong plates 
(Pl. XXXVII. fig. 2%, € XXXVIII. fig. 1 5), slightly divergent, with the spinous 
border directed downward or * ventrad ;’ they recall to mind the pectinate appendages of 
the thoracetron in Scorpio. In Limulus they close or complete the oral armature poste- 
riorly, form the ‘lèvre inférieure” 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 detachedi. The haunch-joints, however, are 
present, though less dentated, in the limb vir. (Pl. XXXVII. fig. 5,1); 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 distinet pair of 
nerves (Pls. XXXVII. & XXXVIII. fig. 1, n *), arising between the origins of the 
main nerve of the limb vir. and that of the ganglionic chord, suggestive of a serial 
homology with the palpal nervules. I am not, however, satisfied with this as a ground 
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 afford advantageous attachments to muscles ; 
other tracts are elevated to support the eyes, as outlooks, and also bearing defensive 
spines. 
The ocelli (æ 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 whieh the dorsal surface of that broad semilunar shield slopes rapidly down to 
the curved digging-edge. The larger compound eyes (A 1) are equally 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- 
+ “La lèvre inférieure est en arrière de la dernière paire de máchoires, et formée de deux lames dentelées." Ta. 
bleau élémentaire de l'Histoire Naturelle des Animaux, p. 452 (8vo, 1797). 
+ Cuvier’s * Règne Animal,’ ed. 1828, vol. iv. 
§ Gr. yecAdproy, a small lip. 
