Crusracea. | LOWER PALAZOZOIC ARTICULATA. 135 
Family. LYMNADIAD (J/°Coy). 
Body entirely enclosed in a vertical, bivalve, caleareo-corneous, oblong carapace, opening along the ventral 
margin; head adhering to the carapace; twenty to thirty pair of membraneous respiratory feet ; two eyes, 
either united in one central mass or separate, one soldered to each valve. 
The type of this family is the recent genus Lymnadia; and I think it may include all the so-called 
Cytheree of the Paleozoic rocks, which, as Burmeister suggests, are much more probably Phyllopodous, and 
for which I haye proposed the name Cytheropsis, also the two following genera. 
Genus. BEYRICHIA (MCoy). 
Gen. Char.—Bivalve, rotundato-quadrate or longitudinally oblong, ends unequal ; anterior, posterior, and 
dorsal margins convex, and surrounded by a sharply-defined, narrow, tumid border or rim; ventral margin 
simple, straight, or concave ; sides tumid, strongly divided into lobes by very deep, nearly vertical furrows, 
extending from the ventral more or less towards the dorsal margin. 
Several species of this genus have been figured and described by Kléden, as varieties of his ‘“ Battus 
tuberculatus.” I long ago perceived that the tubercles and furrows being unsymmetrical, the creature could 
not be a Trilobite, and soon recognized its bivalve structure; shortly before I published this genus (Synopsis 
Silurian Fossils, &c.) Dr Beyrich announced a similar observation incidentally in his memoir “‘ Ueber Einige 
bohmish Trilobiten,” but without naming or defining the genus, which I dedicated to him. The thickened 
margin separates it from those carboniferous so-called Cypridinw of Koninck, some of which shew vertical 
furrows from the ventral margin, which latter character separates them, however, from the other crustacean 
bivalves which resemble them in form. An interruption may usually be detected in the sulcus which separates 
the thickened margin from the rest of the shell, at about one-third the length from the anterior end; this 
probably indicates the position of the connecting ligament of the hinge. (See our figures of B. complicata, 
Pl. 1. E. fig. 3, and 3a). I only know the genus in the Silurian rocks. 
Beyricuia Kiopeni (JM‘Coy). Pl. 1. E. fig. 2. 
Ref. and Syn.—Beyrichia Klideni (M°Coy), Synop. Sil. Fos. Irel. p. 58. B. tuberculata and B., gibba. 
Mem. Geol. Surv. Vol. II. Pl. 8. fig. 14, 15.—(not B. tuberculatus of Kléden). 
Sp. Ch.—Valves truncato-orbicular, ventral margin slightly concave; thickened margin very large and 
strong; surface tumid, having a lengthened oval, nearly vertical, tubercle reaching from the ventral two- 
thirds of the way to the dorsal margin, and nearest to the narrow end, surrounded by a very deep and 
wide sulcus confluent with the ventral margin, and helping to define the unequal ended, deeply sinuate, 
uniform contour of each valve. Length about one line and half. 
This species does not exactly accord with any of those figured by Kléden, as varieties of his Battus 
tuberculatus (nearly all of which I have identified myself in the Gothland limestone). I therefore think that 
Mr Salter, in the Survey Reports, and the editors of the Ray edition of Burmeister’s work on Trilobites, 
are not justified in replacing my name as above, by that of ‘“tuberculata (Kléd. Sp.)” Any one atten- 
tively reading the elaborate description, or looking at-the figures given by that author in his rare work, 
the Versteinerungen der Mark Brandenburg, will readily perceive, as I have above mentioned, that his 
Battus tuberculatus includes many species—the peculiarities of which he recognized as varieties; and I may 
further state, that of all his figures (none of which agree exactly with the present species) continental 
geologists generally apply his specific name to his fig. 22 only, which best deserves the name, and is the 
most common in the Gothland beds, though not yet recognized in Britain. 
I have not seen the granulation of the surface figured in the Mem. of the Geol. Survey. The B. 
gibba figured by Mr Salter in that work is a very trifling variety of this species. His B. plicata of the 
Ray edition of Burmeister seems to be the same differently observed, and is, I think, only an elevated variety 
( the female), 
