218 ' REPORT—1883., 
Hymenocaris, Salter, 1853. 
This paleeozoic Phyllopod was first noticed and named by Mr. J. W. 
Salter in the Report of the British Association (Belfast Meeting) for 
1852, ‘ Trans. Sect.’ pp. 57, 58. Its very common species H. vermicauda 
was more fully described, with figures, by Salter in the ‘Memoirs of the 
Geol. Survey Great Britain,’ &c., vol. iii, 1866, p. 293; t. 2, f.1-4; 
t. 4, f. 25. It has been found in the Lower Lingula-flags of North Wales. 
The terms of generic description are— 
‘Carapace ample, semi-oval, narrowed towards the front, curved 
downward at the sides, but not angularly bent along the dorsal line; no 
external eyes; antenne?; abdomen as long as, or longer than, the cara- 
pace; of nine transverse segments, the last with three pairs of unequal 
lanceolate appendages.’ 
Hymenocaris vermicuuda, Salter, 1853, has its carapace folded or bent 
along the back, so as to form two symmetrical valve-like sides, somewhat 
resembling saddle-flaps, obliquely rounded or semi-elliptical below, and 
with a very slightly convex dorsal line. The curvature of the ventral 
edge varies in fulness and in obliquity with individuals, and is nearly 
always modified by the pressure to which the schist containing the fossils 
has been subjected. The specimens are all flattened ; some are lengthened, 
and some shortened, according to their position relative to the direction 
of the squeeze; and nearly all are crumpled or ‘ plaited’! with parallel 
foldings, coarse or fine, at right angles to the line of lateral pressure. 
Some of the best preserved individuals measure ;®, inch, others 1 
inch, and others (imperfect otherwise) even more, along the back line. 
Those with the first two measurements are 35, inch in height; and their 
angular length (from antero-dorsal to postero-ventral points) is 1,3, inch. 
Many smaller individuals occur. 
The carapace was thin (hence the name=‘membranous’). No 
definite structure has been observed; but Salter noted ‘short wavy lines ” 
on the carapace and the abdominal segments (op. cif. p. 294), and a mars 
ginal furrow along the posterior border of the valves (p. 293). 
Owing to the compressed condition of the schists,” it is diffieult to 
define the original outline of the ends of the carapace. The fig. 4 in pl. 2, 
‘Mem. Geol. Surv.’ iii., is a restoration, and its truncate anterior end is 
a very doubtful feature. The outline given of a specimen shown in fig. 3, 
loc. cit., is not supported by the specimen itself. The front angle, though 
often modified or suppressed by the imperfect cleavage of the schist, is 
sometimes perfect enough to show that it was mueh sharper than in the 
fig. 4 referred to above, in which the truncation is probably due to 
fracture of the specimen taken as the type. The posterior margin usually 
appears to have sloped downwards and outwards, with a bold ventral 
curve, but without the elegant sinuous (ogee) bend, under the dorsal 
angle, which Ceratiocaris usually exhibits. 
The relative position of carapace and body-segments has been sub- 
jected to much interference, between the death and the imbedment of 
the specimens, from the decomposition of the soft parts or connecting 
tissues, and the shifting of the harder relics; yet Mr. Salter’s determina-. 
tion of the more truncate or wider (higher) end of the carapace being the 
1 Salter, Quart. Journ. Geol. Soc., vol. x., 1854, p. 209; and Mem. Geol. Surv. iii. 
1866, p. 247, note. 
2 Throughout this Report the author denotes by the term schist an imperfectly 
cleaved mudstone, not a foliated rock. 
