436 CARBONIFEROUS LAMELLIBRANCHIATA. 



SoLENOMYA (?), J/feA", 1875. Ohio Pal., vol. ii, p. 339. 



— Armstronr/, Young, and Eobertson, 1876. Cat. West. Scott. Fossils, 



p. 55. 

 SoLEMYA, Bigshy, 1878. Thesaurus Devonico-Carboniferus, p. 313. 



— Baity, 18S0. Mem. Geol. Surv. Ireland, Expl. of Sheets 42 and 54, 



p. 22. 



— de Koninck, 1885. Ann. Mus. Eoy. Hist. Nat. Beige, vol. xi, p. 119. 



— Etheridge, 1888. Brit. Foss., pt. 1, Palajozoic, p. 291. 



Janeia, Beusliaitsen, 1895. Abh. Konig. Preuss. Geol. Landesanstalt, n.F., Heft 



17, p. 290. 

 — Woltersiorff, 1899. Unterearbon Magdeburg-Neustadt und seine 



Fauna, ]). 99. 



Generic Characters. — Shell elongated, very inequilateral, anterior end much 

 longer than the posterior, both ends gaping. Surface marked by obscure con- 

 centric lines and well-marked ribs, radiating forwards from the umbones. 

 Anterior adductor muscle-scar elongate and pear-shaped, shallow; the posterior 

 scar round and deeper. Shell thin, periostracum well develojDed and overlapping 

 the margins. 



Observations. — King proposed to give the name Janeia to the Palaeozoic forms 

 of Solenomya, but gave no reasons for his suggestion, and the name has been 

 completely in abeyance until Beushausen emended the description in 1895. This 

 author discusses at length (ojj. cit.) the reasons which have induced him to con- 

 sider that the Palseozoic and recent forms of Solenomya, should be separated into 

 two genera. He states that the Palgeozoic forms are inequivalve, and that the 

 right valve is always overlapped by the left, and that the shell ma}^ or may not 

 gape at either end. 



It cannot be denied that a large number of specimens of Solenomya yrimdeva 

 have the left valve overlapping the umbo of the right ; and de Verneuil has drawn 

 attention to the same fact {op. cit.). M'Coy states, "In all our numerous 

 specimens the left valve is larger at the beak than the right one; " but he says 

 nothing about the overlapping. 



My own opinion is that the overlapping of the valves is an accident, largely due 

 to the fact that the shells were edentulous. Many specimens of Edmondia ohlonga, 

 E. rudis^ E. unioniformis, and other species show the same slipping of the valves, 

 and here there is no question of the valves being unequal. I have, too, a specimen 

 of Solenomya excisa from Tournai, where the right valve has slipped over the left. 

 Now, granting that the valves have slipped on each other, such a condition would 

 obliterate the gaping of the ends of the shell by bringing the anterior and posterior 

 edges respectively into contact with each other, so that it is very probable that 

 both the characters on which Beushausen relies to distinguish the Palaeozoic from 

 the recent Solenomyse are due to the same accidental cause. 



