7A, REPORT—1868. 
Trias are the long intervening series of Upper Silurian, Devonian, Carboni- 
ferous, and Permian formations. I consider this form may more properly 
be placed with Bunodes, Hemiaspis, &c. among the aberrant forms of the 
Limulide, of which it may possibly have been a larval state. 
Among the Secondary forms of Crustacea I have described the following 
from British specimens during the past year. 
Palinurina longipes. Lower Lias, Lyme. (Geol. Mag. 1868, vol. v. 
p. 260, pl. 14. fig. 5.) 
Pseudoglyphea grandis. Lower Lias, Weston. (Ibid. p. 353, pl. 17. fig. 1.) 
Glyphea rostrata, Lower Lias, Weston. (Ibid. p. 354, pl, 17. fig. 2.) 
Heeri. Lower Lias, Lyme Regis. (Ibid. p. 355, pl. 17. fig. 3.) 
Tomesii. Lower Lias, Welford Hill, Stratford-on-Avon. (Ibid. 
p. 356, pl. 17. fig. 4.) 
I have now to notice another species, of the genus Penewus of Fabricius, 
from the Lower Lias, Northampton. This is a remarkably persistent form ; 
and the genus is actually found now living in the Mediterranean, if Dr. 
Oppel’s determination be correct, which I feel little doubt in endorsing. 
This handsome Crustacean (see Plate IL. fig. 3) was not less than 94 
inches in length when measured along the dorsal line, the carapace being 
about 3 inches, and the abdomen 63 ; the rostrum was very strongly serrated 
as in the Palemonide, but the serrations have been abraded in the fossil. 
This form most nearly resembles in size and appearance the Peneus speciosus 
of Minster, but differs slightly in the form of the border of the abdominal 
segments, and also in the direction of the strong and deeply forked sulcus 
which marks each side of the latero-anterior portion of the carapace near 
the base of the great antenne. The surface of the carapace and segments 
was highly enamelled, some portions of which may still be observed in the 
fossil. Ihave named it Penceus Sharpii, after Mr. Samuel Sharp, F.G.8., who 
is the discoverer of the fossil. 
Of the Cretaceous Crustacea two have been noticed by me, viz. a new 
Cirripede from the Norwich Chalk, Pyrgoma cretacea (Geol. Mag. vol. y. 1868, 
p. 258, pl. 14. figs. 1 & 2), and Necrocarcinus tricarinatus, from the Gault 
of Folkestone (ibid. p. 259, pl. 14. fig. 4). 
I am now enabled to add two new species of a family not hitherto before 
noticed in a fossil state in Britain, the family of the Thalassinide. 
This curious group contains several genera and species. Those of which 
we know the habits, burrow in the sand, which they readily excavate with 
their feet. 
Although frequently found fossil, especially in the Upper Chalk of Maes- 
tricht, of France, and Bohemia, we rarely see atrace of their bodies. Even 
in dredging, the usual thing is to find the two fore claws only in the dredge 
(if any part of them is taken at all). In the fossil state it is to be also 
anticipated that their occurrence would be rare, as the integument of their 
bodies (like that of the Hermit-Crab and others which conceal themselves 
in foreign substances) is extremely thin, and often soft. I may compare 
the difference of their test to that which exists between a lady’s hand encased 
from infancy in a kid glove, and the hand of a savage who uses his digits 
constantly for delving in the ground after roots. In the one, the covering 
membrane is thin and soft; in the other, hard and horny. One might even 
go further and imagine (hy repeated exclusion from use) the nails would 
be no longer developed; certainly they are less powerful as offensive weapons. 
This is precisely what we find does take place in the burrowing Crustacea ; 
