OF THE ORDER MEROSTOMATA. 9 
Order—MEROSTOMATA, Dana, 1852. 
Having the mouth furnished with mandibles and maxillz, the terminations of which 
become walking or swimming feet and organs of prehension. 
I. Sub-Order—Hvuryprzripa, 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 (oced/z) near the centre, and a pair of large marginal 
or subcentral eyes ; the mouth furnished with a broad post-oral plate, or mefastoma, 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. 
Il. 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 oce//i 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. 
Norr.—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 Hurypterida 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 Mrrostomara—a name 
proposed by Dr. J. D. Dana for the recent King-crabs only, retaining at the same 
time the names Lurypterida 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. 
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