New or Little-knoiun Victorian Fossils. 67 



from the posterior margin, directed backward. Foramen ellip- 

 tical, with a post-apical groove which partially interrupts the 

 lines of growth passing down towards the posterior margin, and 

 emerging on the interior in a sipho. Surface gently convex on 

 the anterior slope, abruptly depressed in the post-apical region. 

 Surface with numerous, fine, concentric growth lines. Outline of 

 brachial valve broadly elliptical ; apex centric, conical and 

 strongly convex anteriorly, somewhat depressed in the post-apical 

 region, liut recovering its convexity near the posterior margin. 

 Concentric lines of growth distinct. 



The figure (5) of the pedicle valve is from an obliquely crushed 

 specimen. 



Measurements. 



Length of pedicle valve figured - - 6.5 nun. 



AVidth of pedicle valve figured - - 3 ,, 

 Length of brachial valve figured - - 6 ,, 



Width of brachial valve figured - - 4..5 ,, 



Height of brachial valve figured - - 1.5 ,, 



Observations. — The genus Orbiculoidea has been usually 

 regarded by palaeontologists as a sub-section of Di-scina, Lam.arck. 

 The researches of Mr. W. H. DalP, tend to show that the type 

 species of Discini is D. striata, Schumacher sp. (non Sowerby) 

 — D. ostraeoides, Lam., a recent form from West Africa and 

 apparently the only representative of the genus. One of the 

 chief distinctions between Discina and Orbiculoidea, pointed out 

 by Messrs. Hall and Clarke", is the relative position of the 

 perforation and and tlie direction of the pedicle furrow and tube. 

 In Discina the pedicle valve is perforated behind the apex and 

 the pedicle emerges antero-posteriorly. The rever.se is the case 

 in Orbiculoidea, the pedicle furrow, situated just below and 

 behind the apex and extending over a gieater or less portion of 

 the valve, emerging postero-anteriorly. The furrow terminates in 

 a tubular sipho which nearly reaches the margin of the shell 

 Often there is a callosity surrounding the greater part of the 

 internal tube. This structure is well shown in one of our speci- 

 mens (Fig. 12). 



1 Bull. Mus. Comp. Zool., Harvard Colleg'e, 1S71, vol. iii., No. 1. Hall and Clarke : Palae- 

 ontology of New York, 1892, vol. viii., Palaeozoic Brachiopoda, pt. i., p. 121. 

 '- Oy. fit., p. 125. 



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