72 : REPORT—1868. 
Fourth Report on the Structure and Classification of the Fossil 
Crustacea. By Henry Woopward, F.G.S., F.Z.8., of the British 
Museum. 
. (Puate IT.) 
Durie the past year no new Silurian forms of Crustacea have come under 
my notice, save the series which I had the pleasure to exhibit at Dundee. 
Of these, belonging to the Order Merostomata, the following have been 
fully described and figured :— 
a. EURYPTERIDE*. 
1 Eurypterus (Pterygotus) punctatus, Salter, sp, 
scorpioides, sp. NOY. 
3. obesus, Sp. Noy. 
4. Pterygotus raniceps, sp. nov. 
6. LimvLtm2z7f. 
Neolimulus falcatus, sp. et gen. noy. 
Perhaps the most interesting point which I have been able to determine 
in connexion with these Upper-Silurian forms is the occurrence of gill-plates 
in Pterygotus in precisely the same relative position as we find they occupy 
in Limulus at the present day, but differing in form. These leaf-like 
branchiz occur in rows, and still exhibit their highly vascular structure, and 
indicate by their aspect in the fossil state their extreme tenuity. 
It is very interesting to me, and I cannot but pelieve that it will also in- 
terest others working at the Znvertebrata, to find the number of points which 
Pterygotus possesses in common with the Scorpionide among the Arachnida. 
If the organs called “combs,” which are attached to the first thoracic seg- 
ment of Scorpio, be rudimentary gills, not wholly aborted, we have another 
point of analogy gained between the two f. 
That rudimentary gills existed in Pterygotus at the border of the segments, 
and in that position in which the pulmonary sacs in Scorpio are found, I 
have evidence both from the Devonian and Silurian species. 
The position also of the ovaries in Pterygotus and Scorpio is the same, 
though in the former the opening to the sacs is double, as in Limulus and 
other Crustacea, whereas in Scorpio it is evternally central as in Insects. A 
bilobed plate conceals the apertures in both forms. My conclusion is that 
there is good ground for assuming that Pterygotus represented, in Palaeozoic 
time, the aquatic condition of Scorpio, just as the aquatic larvee of Lzbellula 
represent to day the imago of a future season. 
I have lately received specimens from the Carboniferous shales of Carluke 
of a new form of Crustacean allied to Cyclus. I was at first doubtful whe- 
ther the Cyclus radialis of M. de Koninck, from Belgium, really represented 
the Agnostus radialis of Prof. Phillips, from the Carboniferous Limestone of 
Bolland, Yorkshire. I have fortunately been able to see and examine the 
original specimen of Cyclus radialis of De Koninck, and find that it does agree 
with the figure in Phillips’s ‘ Geology of Yorkshire’ (vol. ii. t. 22. fig. 25) ; 
but it entirely disagrees with M. de Koninck’s magnified figure. I have 
therefore redrawn the Belgian form, and propose to figure it by the side 
of the new British form from Carluke. (See Plate II. figs. 1 & 2.) 
* See Quart. Journ. Geol. Soc. 1868, vol. xxiv. pp. 289-294, pls. 9 & 10. 
+ See Geol. Mag. 1868, vol. v. p. 1, pl. 1. figs. 1 & la. 
I am preparing injections of recent specimens of Scorpio in the hope of being able to 
demonstrate this point certainly. 
