82 CARBONIFEROUS TRTLOBITES. 



Trilobites ; and the large, kidney-shaped, faceted eyes recall those of Calymene ; 

 moreover, there is a facial suture across the cheeks, as in Trilobites, so that, were 

 it not for the presence of the antennae, which project from the lower side of the 

 anterior margin of the buckler in two unequal pairs, these resemblances would 

 amount to an absolute identity of structure. As it is, the presence of an 

 hypostome in the same position as that piece of the mouth is found in Trilobites, 

 renders the similarity of this extinct type of Crustacea still more striking, while 

 the antennas exhibit an unmistakable resemblance to the Isopods. 



" In view of the synthetic character of these structural features it should not be 

 overlooked that the buckler of our new Crustacean, for which I propose the Dame 

 Tomocaris Peircei, extends sideways into a tapering point, curved backwards over 

 the first thoracic ring, as is the case with a great many Trilobites. The thorax 

 consists of nine rings, seven of which have prominent lateral points, curved 

 backwards like the pleurae of Olenus, Lichas, &c. The sixth ring is almost 

 concealed between the fifth and seventh, and is destitute of lateral projections, as 

 is also the ninth. Those rings are distinctly divided into three nearly equal lobes 

 by a fold or bend on each side of the middle region, so that the thorax has the 

 characteristic appearance of that of the Trilobites, to which the latter owes its 

 name. The legs are very slender, and resemble more those of the Copepods and 

 Ostracods than those of any other Crustacea. There are nine pairs of them, all 

 alike in structure, six of which, however, the anterior ones, are larger than the three 

 last, which are also more approximated to each other. Besides the legs there is a 

 pair of maxillipeds attached to that part of the buckler which extends back to the 

 facial suture. These maxillipeds resemble the claw of a Cyclops. All these 

 appendages are inserted in that part of the rings corresponding to the bend of the 

 thoracic lobes ; so that if there exists a real affinity between the Trilobites and our 

 little Crustacean — and their resemblance is not simply a case of analogy — we 

 ought hereafter to look to a corresponding position for the insertion of the limbs of 

 Trilobites. I do not remember with sufficient precision what Billings, Dana, and 

 Verrill have lately published concerning the limbs of Trilobites to say now what 

 bearing the facts described above may have upon the subject as lately discussed in 

 ' The Journal of Science.' But of one thing I am satisfied, since I have examined 

 the Tomocaris Peircei that Trilobites are not any more closely related to the 

 Phyllopods than to any other Entomostracae, or to the Isopoda. In reality the 

 Trilobites are like Tomocaris, a synthetic type, in which structural features of the 

 Tetradecapods are combined with characters of Entomostraca and other 

 peculiarities essentially their own. 



" The pygidium or abdomen of Tomocaris is very like the abdomen of the 

 ordinary Isopods with an articulated oar attached sideways, and leaf-like 

 respiratory organs upon the under side. The whole pygidium is embraced 



