66 BRITISH FOSSIL CRUSTACEA. 
Pl. XIII, where the anterior thoracic segments are displaced, yet its exact contour 
cannot very well be represented. 
The anterior body-segments are much arched forward in the centre; the lateral area is 
recurved as in the other species ; and the anterior border appears to have projected under and 
formed an articulation with the preceding segment (see Pl. XV, fig. 1, segments 9 and 10). 
The sculpture of the body-rings (Pl. XIII, fig. 1 gy) extends over less than half their 
surface. 
The plicee are open forwards, very small, often almost linear on the front margin, 
and the remainder are less than semicircles. The anterior border of the segments is 
rounded off and smooth. A transverse faintly impressed line separates the anterior 
sculptured half from the posterior smooth portion; but this is not always seen. The 
lateral borders of the segments are not crenated. 
The telson (PI. XV, fig. 2, 20), is bilobed in form like the preceding varieties a and 8 ; 
and the penultimate segment has its anterior border contracted, its sides curved, and its 
posterior angles produced in a similar manner. 
On the Branchie in Pterygotus.—The determination by Dr. James Hall, in America, 
of the true position of the thoracic plate or operculuin in Lwrypterus,! having since been 
fully confirmed with regard to the British species of Pterygotus,? Slimonia,? and Hury- 
pterus,* and also its homology with the operculum in Zemualus (Pl. IX, fig. 1, 1 a)— 
beneath which are placed the respiratory organs—it was reasonable to expect to find 
evidence of branchiz in Pterygotus also, considering the wonderful state of perfection 
in which many of the remains of this genus have been preserved. 
But it was not until 1867 that I obtained satisfactory evidence of their existence. 
I first drew attention to them in my ‘Third Report to the British Association on the 
Structure and Classification of the Fossil Crustacea,’ at Dundee, in September of that 
year, and I have since published figures of some detached leaflets in a paper read before 
the Geological Society in March last.° 
I first detected them associated with the specimen figured in Pl. XII, figs. 1 @ (ér) 
and 1d; next in that in Pl. XIII, figs. 1 @ and 1 4. When at Dundee (in 1867), 
I obtained from Mr. Slimon a portion of shale having several detached leaf-like organs 
preserved upon it,’ corresponding in form and surface-markings with those referred to 
above, and which occur with specimens of entire Pterygoti and lymg in such a position 
upon the slabs as to leave little doubt that their normal place of attachment would be 
under the thoracic plate or operculum, as in the recent Zimulus. 
1 Hall, 1859, ‘Geol. Surv. New York,’ “ Paleontology,” vol. iii, pp. 392—413. 
2 H. Woodward, 1867, ‘ Quart. Journ. Geol. Soc.,’ vol. xxiii, pp. 28—37, pls. 1 and 2. 
5 Ditto, ‘Intellectual Observer,’ 1863, vol. iv, pp. 229—237. 
* Ditto, ‘Geol. Mag.,’ 1864, vol.i, pp. 107—111, pl. vy, fig. 8. 
® * Quart. Journ. Geol. Soc.,’ 1868, vol. xxiv, p. 294, pl. x, figs. 3a, 3d. 
6 The same which are figured in the ‘ Quart. Journ.’ above referred to. 
