186 BRITISH FOSSIL CRUSTACEA. 



shell of which the soft parts of the animal are completely enclosed (see PL XXXIV, 

 figs. 1 and 2, and PI. XXXVI, fig. 1) — the gnathopods or jaw- feet are ranged. These 

 organs fulfil, as in the Eurypterida, the combined functions of locomotion, prehension, 

 and so much of the sorting and mastication of the food as is needful before deglutition. 

 They are all chelate, the most anterior pair, PL IX, figs. 1, 2 (the antennules), is the 

 smallest, and is prae-oral, being attached on either side of a minute epistome, the 

 antennules are not provided with a spinose coxal joint, as is the case with the five 

 succeeding pairs. The second pair is subject to modification in the males of the 

 American species, PL IX, fig. 1 a (Limulus polyphemus), and the second and third in the 

 males of the Moluccan species (L. moluccanus). The sixth pair of limbs have stronger 

 maxillary joints, and at the distal extremity (PL XXXIV, fig. 4) bear upon the ante- 

 penultimate joint a series of lamelliform plates, which, when spread out, greatly assist 

 the animal both in burrowing and walking 



This, with a small bifid metastome, 1 completes the circumoral appendages. 



Behind the mouth are placed six broad, lamelliform appendages, the first of which 

 bears upon its upper and inner surface the ovaries or reproductive organs, and the 

 remaining five the branchiae (see PL XXXV, figs. 1, 6, and 8). 



The following details of the internal structure of the living Limulus I take from 

 Professor Owen's valuable Monograph " On the Anatomy of the American King Crab, 

 Limulus polyphemus" ('Trans. Linnsean Soc.,' 1872, vol. xxviii, pp. 459 — 506), to whose 

 kindness, and also to the courtesy of the President and Council of the Linnaean Society , 

 I am indebted for permission to reproduce the subjects forming Plates XXXIV, XXXV, 

 and XXXVI of the present Monograph. 



On the Anatomy of the American King-Crab, Limulus polyphemus, Latr. By 

 Professor Owen, C.B., F.R.S., E.L.S. 



§ 1. " Muscular system. — The parts sent inward from the crust or exoskeleton are those 

 that afford attachment to muscles, and those which also form or contribute to the joints 

 of the articulate appendages. They are termed ' entapophyses ' and ' apodemes.' The 

 ' apodemes ' that relate to the cephaletral 2 limbs (PL XXXVI, n — vi) are broader and 

 more complex than those of the thoracetron (ib., vn — xm). The most conspicuous 

 entapophyses are the following : — A pair of oblong, lamelliform processes descend from 

 the segment confluent with, and forming part of the hind border of the cephaletron 2 at 

 the parts indicated by the ciliate depressions. Six pairs of similar, but rather smaller 



1 Named by Prof. Owen " chilaria," from XeiXapiov, a small lip. 



2 Prof. Owen has proposed in his ' Memoir,' from which we quote so largely, the use of the terms 

 "cephaletron" for the seven anterior somites forming the cephalic shield; "thoracetron" for the seven 

 succeeding somites forming the thorax or middle body ; and he applies Spence Bate's term " pleon " for 

 the hinder apodal portion of the posterior shield, or abdomen, " including therein the part which Spence 

 Bate calls ' telson,' constituting the characteristic 'tail-spine' of the present singular genus." 



