44 DEVONIAN FAUNA. 
II. Family. — MiTiLiDiH, Fleming, 1828. 
1. Genus. — Hoplomytilus, Sandherger, 1853. 
Sandberger founded this genus for equivalve, triangular, arching mussels, with 
sharp umbones situated at the extreme anterior point, and with a hinge which 
bears an elongated septum under the beak, behind which is a linear transverse 
tooth on the right valve and a corresponding groove on the left. 
The inferior parts of the shell appear to be unknown. 
It occurs in the Devonian rocks. 
1. Hoplomytilus crassds, Sandberger, PI. IV, figs. 2, 2 a, 3, 3 a. 
1853. Hoplomytilus ceassus, Sandlerger. Verst. Ehein. Nassau, p. 281, 
pi. xxiz, figs. 13, 13 a — c. 
1884. — — Tryoii. Structural Conch., vol. iii, p. 267, 
pi. cxxix, fig. 26. 
1889. — — Wliidlorne. Geol. Mag., dec. 3, vol. vi, p. 78. 
1891. — — FrecTi. Abhandl. Geol. Specialk.Preuss., Baud ix, 
pt. 3, p. 161, fig. 19. 
Description. — Right valve large, rather flat, recurved. Umbo small, sharp, 
proximate, forming the extreme anterior point of the hinge-margin. Hinge- 
margin slightly convex. Hinge consisting of a low, flattened, elongate, 
triangular flap or interior ligamental area, free on the lower and posterior 
sides, above which are three very elongate, narrow, lateral teeth, which 
are nearly parallel to the margin, and are separated by broad concave grooves. 
Anterior margin very concave. Line of greatest elevation arching backwards 
from the umbo very near and almost parallel to the anterior margin, and rendered 
angular by a flattened oblique surface in front, which is in turn bounded by 
another ridge about halfway to the margin, within which the shell recedes so 
as apparently to form a long, lanceolate lunule. Surface, behind the line of 
greatest elevation, sloping gently and flatly to the margins. Ornament, and 
posterior and inferior regions unseen. Shell-structure very thin except on the 
margins. 
Size. — Large : the specimens are too defective for measurement. 
Locality. — Wolborough. There are three specimens in the Museum of Practical 
Geology, and three specimens in the Woodwardian Museum. 
