[ 459 ] 
M On the Anatomy of the American King-crab (Limulus polyphemus, -— 
By Prof. OWEN, F.R.S., F.L.S., $c. 
(Plates XXXVI.-XXXIX.) 
Read December 21st, 1871, and January 18th, 1872. 
$ L Introduction.—The living representatives of extinct groups of animals have always 
had peculiar attractions for my scalpel, especially when the lost group was large and the 
dissectible representative rare and exceptional in character. Such, e. g., was the Kivi*, 
sole survivor of the race of Moas ; such the Protopterus or Lepidosirent, the living repre- 
sentative of extinct notochordal, protocercal, cycloganoid fishes of palseozoic seas ; such 
the Nautilus, in like relation to the extinct fabricators of chambered and siphonated 
shells t; such also were Terebratula, Lingula, and Discina $, as representatives of the 
Brachiopoda. 
With reference to the singular and interesting palzeozoic Crustacea known chiefly, if 
not exclusively, in 1840, as * Trilobites, I was for a time uncertain whether to take the 
rare Isopod Serolis, of which a specimen was procured for me for that purpose by my 
friend Charles Stokes, Esq., F.R.S., the discoverer of the ‘labium’ or lip-plate in Trilo- 
bites (Asaphus platycephalus)||, or to look for their grade and plan of internal structure 
in Limulus. . 
The authority of W. Sharpe Macleay, after the appearance of his famous * Hore 
Entomologicze,”” weighed about that time heavily upon us. All who had studied the 
Trilobites up to 1843 were of opinion that they were malacostracous. Audouin led the 
way by affining them to the Isopoda Y ; and Macleay, in an Appendix to Murchison's 
great work on the Silurian strata, assigned to Trilobites a position as a distinct Order 
between the Isopoda and Aspidophora, basing his views on the trilobed character of the 
segments in Serolis and Bopyrus, and the character of the eyes in Cymothoa, which ** were 
large, sessile, and compound, as in Trilobites. Moreover Cymothoa and other Isopods," 
he remarked, * rolled themselves into a ball," as Trilobites have been found to do before 
they perished. 
The first general fact or view which influenced my choice in this matter was the 
character of the Malacostraca, founded on the number of body-segments,—seven for 
* «On the Anatomy of the Apterya australis," Trans. of Zool. Soc. vols. ii. & iii. (1838). 
+ Trans. Linn. Soc. vol. xviii. 1839 
+ ‘Memoir on the Pearly Nautilus (Nautilus pompilius), 1832. 
§ “On the Anatomy of the Brachiopoda of Cuvier," Trans. Zool. Soc. vol. i. (1835); also ‘On the Anatomy of 
Terebratula and Lingula, Monograph, published by the Palæontographical Society in vol. for 1854. (The subjects 
for the anatomy of Discina, Sow., were referred to the genus Orbicula.) 
|| Trans. Geol. Soc. Lond., N. $. vol. i. pl. 27. 
€] « Recherches Sur les Rapports Naturels qui existent entre les Trilobites et les Animaux Articulés,” Annales des 
Sciences Physiques de Bruxelles, tom. viii. (1821). 
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