334 CARBONIFEROUS LAMELLIBRANCHIATA. 



Sub-genus Scaldia, de Bycl-holt, 1852. 



Scaldia, de Byckholt, 1852. Melanges paleontol., le partie, pi. x, figs. 24 — 26; 

 2e partie, p. 67. 



— S. P. Woodward, 1851-6. Manual of Mollusca, p. 498. 



— Biysby, 1S77. Thesaurus Devonico-Carboniferus, p. 311. 



— de Koninck, 1885. Ann. Mus. Koy. d'Hist. Nat. Belgique, torn, xi, p. 54. 



— Fischer, 1887. Manuel de Concbyliologie, p. 1100. 



Generic Characters. — Shell subcircular or oval, equivalve, slightly inequi- 

 lateral, moderately gibbose. Umbones subcentral, small. No lunule or escutcheon. 

 Ligament external, small, contained in a very narrow groove just above the edge 

 of the hinge. 



Interior. — Adductor muscle-scars shallow, more or less rounded. Pallial sinus 



entire. Hinge-line simple, erect, with a single tooth in each valve under the 



R 1 

 umbo. Formula : ' ' . There is a thickened, depressed, vertical plate, much 

 Li. 1, 



hollowed internally, the free edge of which extends outwards into the cavity of 



the umbo. 



Externally the surface is almost smooth, or ornamented by numerous fine 

 concentric lines. 



Observations. — This genus was established by de Ryckholt {op. supra cit.), and 

 the type was Scaldia Kiclcxiana ; but de Koninck considers this species to belong 

 to Edmondia, but retains the genus for the six other species originally referred to 

 it by de Ryckholt. In the original description the genus is said to have a 

 sinuated pallial sinus, but de Koninck has shown that this was an error. I am 

 not strongly convinced of the value of this genus, which differs from Edmondia 

 in its more orbicular shape, and in the possession of a cardinal tooth in each 

 valve; but, as I have said (ante, p. 290), I have seen specimens of Edmondia 

 Kiclcxiana which occasionally show a rudimentary cardinal tooth. De Koninck, 

 however, will not allow that this is the case, for he says, speaking of the type of 

 Ryckholt's S. Kichciana, " II a considere comme dent un faible renflement de la 

 lame cardinale, comme le prouve Pexemplaire merae dont il s'est servi pour decrire 

 et figurer l'espece." De Ryckholt's figure shows the muscle-scars and sinuated 

 pallial line very prettily, but no indications of these characters are shown in 

 the type. 



I have retained the term Scaldia as a sub-genus of Edmondia, following Wood- 

 ward, and regard the hinge and suborbicular shape as important characters for the 

 separation of the two genera. 



