280 AVICULID^. 



HoRNESiA, Laube, 1866. 



Etym. — Dedicated to Dr. Moritz Homes. 



Syn. — Goniodus, Dunker. 



Obliquely elongated, solid, ineqiiivalve, left valve inflated, 

 •with incurved beak, right more or less flattened, hinge-line 

 straight, with a short, narrow, somewhat contorted anterior and 

 a long posterior wing, not separated from the body ^f the shell, 

 except by a shallow marginal insinuation ; ligament situated in 

 several pits externallj^ on the hinge-line, one pit being below the 

 beak and. reaching rather internally, one is on the anterior and 

 the remainder on the posterior side ; hinge in the left valve con- 

 sisting of a strong oblique tooth under the beak, separated by a 

 pit from a smaller anterior cardinal ; in the right valve there is 

 only one strong tooth, besides that there are generally numerous 

 crenulations at the margin of the hinge-line in both valves, and 

 one or two oblique submarginal ribs posteriori}^ ; muscular scars 

 two, deep, close together, not far from the umbones. Several of 

 the Triassic species of Gervillia, most likelj^, are referable to 

 this group. 



Differs from the t3q3ical Gervillise hy the peculiar structure of 

 the hinge, and by a more or less lengthened septum going 

 through the cavity of the umbones. 



AcTiNODESMA, Saudberger, 1856. 



Biatr. — A, malleiforme ^ Sandb. Devonian ; Germany. 



Slightly obliquely and broadly oval, moderately convex, with 

 a long, straight hinge-line, produced on either side into a narrow 

 wing, hinge with a number of ribs inclined towards the horizontal 

 hinge-line on either side of the central area on which they are 

 absent ; these ribs are separated by grooves in which the liga- 

 ment is said to be lodged, being almost quite internal. 



Stoliczka says : " I do not think that it has been sufficiently 

 established that the grooves alluded to are really ligament or 

 cartilage-grooves. They rather appear to me to be identical 

 with similar hinge-ribs of Pterinea and Gervillia, and the liga- 

 ment may have been external and marginal, attached to the 

 thickened margin of the shell which slopes internall}^, as is, for 

 instance, the case in most species of Avicula and particularly in 

 the Meleagrina group." 



Subfamily YVLHELLINM. 



Ligament lodged in a special single groove or pit, extending 

 from the beak internally. 



Vulsella, Lam., 1799. 

 Syn. — Reniella, Swainson, 1840. 



Distr. — 7 sp. Red Sea, India, Australia, Tasmania. Fossil, 

 7 sp. Eocene — ; Britain, France. V. rugosa, Lam. (cxxxi, 66). 



