﻿OF THE ORDER MEROSTOMATA. 9 



Order— MEROSTOMATA, Dana, 1852. 



Having the mouth furnished with mandibles and maxillae, the terminations of which 

 become walking or swimming feet and organs of prehension. 



I. Sub-Order — Eurypterida, Huxley, 1859. 



Crustacea with numerous free thoracico-abdominal segments, the first and second (?) 

 of which bear one or more broad lamellar appendages upon their ventral surface, the 

 remaining segments being devoid of appendages; the anterior rings united into a 

 carapace bearing a pair of larval eyes {ocelli) near the centre, and a pair of large marginal 

 or subcentral eyes ; the mouth furnished with a broad post-oral plate, or metastoma, and 

 five pairs of moveable appendages, the posterior of which form great swimming feet ; the 

 telson, or terminal segment, extremely variable in form ; the integument characteristically 

 sculptured. 



II. Sub-Order — Xiphosura, Gronovan, 1764. 



Crustacea having the anterior segments welded together to form a broad, convex 

 buckler, upon the dorsal surface of which the compound eyes and ocelli are placed, the 

 former subcentrally, the latter in the centre in front ; the mouth furnished with a small 

 labrum, a rudimentary metastoma, and six pairs of moveable appendages. Posterior 

 segments of the body more or less free, and bearing upon their ventral surfaces a series 

 of broad lamellar appendages, the telson or terminal segment ensiform. 



Note. — Having long been convinced of the propriety of expressing in some suitable 

 manner the correctness of the conclusions of Professors Agassiz and James Hall as to the 

 close affinity existing between the Eurypterida and the Xiphosura, and being fully 

 persuaded at the same time that they naturally form two distinct, although closely 

 related groups, I have ventured to unite them in the Order Merostomata — a name 

 proposed by Dr. J. D. Dana for the recent King-crabs only, retaining at the same 

 time the names Eurypterida and Xiphosura, as sub-orders ; sufficient evidence for the 

 correctness of which I trust to be able to bring forward before the completion of this 

 Monograph. 



2 



