200 ON THE ANATOMY AND AFFINITIES OF 
No Copepod, so far as I know, presents so great a number as 
twelve free segments behind the carapace. 
No Copepod has its appendages reduced to so few as three or 
four pairs, nor, in any, is one pair of the post-oral cephalic appendages 
converted into the chief organ of locomotion. 
The Pecilopoda (Plate XVI. [Plate 27] fig. 13) are [ believe 
the only Crustacea which possess antennary organs like those of 
Pterygotus, and, like them, have the gnathites converted into loco- 
motive organs, want the appendages to the sixth abdominal somite, 
and present on some parts of the body a remotely similar sculpture. 
In this order, however, we find but a small labrum,—a rudimentary 
metastoma,—a very differently constructed body, and a large number 
of appendages, both thoracic and abdominal, characters which effectu- 
ally preclude the association of the extinct Crustacea under discussion 
with this type! 
The palp of the mandible of Nebalia (Plate XVI. [Plate 27] 
fig. 10) is, in its proportional size and form, not unlike that of 
Prerygotus anglicus, but this is the sole resemblance of importance 
which I can detect between the Branchiopoda and the Prerygett. 
While the relations of the Péerygoti with the great majority of 
other Crustacea are such as, in my mind, fully to justify their 
ordinal separation, there is one small and extinct group, having a 
similar geological range, with which they are undoubtedly closely 
connected. This is the genus Burypterus of Harlan, of which many 
species have now been brought to light. Putting together the 
descriptions of Harlan, Eichwald, Roemer, and others, with the 
results of a personal inspection of some species recently described by 
Mr. Salter, I can only arrive at the conclusion that, in its general 
form and structure, Eurypterus very closely resembled Péterygotus, 
differing from it however as Sapphirina differs from Coryceus, viz., 1n 
having the eyes submedian instead of marginal. The ectognaths of 
Eurypterus appear to have been constructed upon precisely the same 
plan as those of Pterygotus, and its thoracic and abdominal members 
would seem to have been equally undeveloped. Eichwald describes 
1 If the abdominal somites or the Carboniferous BelMnurus, &c. were really free, they 
would present a certain approximation to the Pterygot?, Indeed, the evidence that these 
Csrboniferous Crzzstacea were true Pectlopoda is, to my mind, anything but conclusive. 
” Ferd. Roemer. Ueber ein bisher nicht beschriebenes Exemplar von Eurypterus aus 
Devonischen schichten des Staates New York in Nord-Amerika.—Dunker und von Meyer’s 
Paleontographica, b. 1, 1851, p. 190. 
3 Fichwald’s representation of the under surface of the head is terribly diagrammatic. 
If it be a correct representation of an actual object, it affords evidence of only three pairs of 
appendages. lis “‘ two large, almost semilunar, lateral parts” appear to me to be the basal 
