438 CARBONIFEROUS LAMELLIBRANCMIATA. 



to be anterioi-, the arraugement of the muscle-scars would have a very close 

 resemblance to that which obtains in Solenomya. Of course the well-marked 

 urabones, the internal ossicle, and other characters of E. arcuata sufficiently clearly 

 mark off the shell from Solenomya (compare PL XXXV, figs. 2 — 4, 6, and 7). 



Many of the characters of Solenomya would lead one to suppose that the larger 

 end, as in nearly all Lamellibranchs, was posterior. The shape and nature of the 

 muscle-scar in the short end is identical with the anterior muscle-scar of many 

 Carboniferous genera of Lamellibranchs, and it is bounded on its edge remote from 

 the margin of the valve by a ridge, which leaves a groove in casts. Further, the 

 muscle-scar of the long end of Solenomya has the characters of the posterior 

 adductor, i.e. it is shallow, pear-shaped, placed obliquely, and remote from the 

 margin. As a rule the umbones are directed forwards in Solenomya, and in 

 Carboniferous forms they seem to point backwards. Again, in Lamellibranchs 

 the radiating ribs or strise, when present, slope, as a rule, downwards and 

 backwards. In fact, there is nothing in the shell of the Palseozoic Solenomya to 

 denote that the short end is posterior, but judging from homology, rather the 

 contrary. In recent Solenomyse of course the position of the siphons determines 

 the posterior end of the shell, unless it be the position of the siphons which have 

 changed, and not the shell. I have never yet been able to find the shell with the 

 periostracum preserved, or to obtain any indication that the lower edges of the 

 shell were not in contact, or that there was any great development of periostracum 

 with fringes which overlapped them. 



Solenomya peimj;va, Phillips, 1836. PI. L, figs. 1 — 6. 



SoLEMTA PRiM^VA, PhiJUpx, 1830. Geol. Torks., pt. 2, pp. 209 aud 217, pi. v, 



fig. 6. 



— — Portloch, ISJ-S. Geol. Rep. Londonderry, p. 441. 



— — Morris, 1843. Cat. Brit. Foss., Ist edit., p. 101. 



— PuzosiANA, de Koninch, 1843. Auim. Foss. Carb. Beige, p. 60, pi. v, 



figs. 2 a, b. 

 Sansuinolites eadiatcs, M'Coy, 1844. Sjnop. Carb. Foss. Ireland, p. 50, 



jjl. xiii, fig. 94. 

 Non SoLEMTA pbim^va, de Verneuil, 1845. Geoi. Russia, vol. ii, p. 295, pi. xix, fig. 5, 



— — d''Orlifjni/, 1850. Prodrome paleontol., vol. i, p. 129. 



— PuzosiANA, d'Orhicjny, 1850. Ibid., p. 129. 



— PEiMiEVA, Morris, 1854. Cat. Brit. Foss., 2nd edit., p. 224. 



Non SoLENiMTA ? PRIM^VA, M'Coy, 1855. Brit. Pal. Foss., p. 519, pi. iii, figs. 3, 3 a. 

 — — Eichivald, 1860. Lethsea Rossica, p. 1040, pi. xxxii, 



fiff. 10. 



