CYTHERIDEA. 37 



2 & 2*. Cythebidba Muelleri (Miinster), et var. torosa, Joiiet^. 



Cttheeidea Muelleei, et var. torosa, Jones. Quart. Journ. Geol. Soc, vol. x, 



1854, p. 160, pi. iii, figs. 7, 8 ■} Mem. Geol. Survey, 

 Tert. Fluvio-Marine Form. Isle of "Wight, 1856, 

 p. 158, pi. vii, figs. 27, 28 ; Monogr. Tert. Entom., 

 1857, pp. 41—43, pi. V, fig. 4, and pi. vi, figs. 10—13'; 

 Brady, Trans. Zool. Soc, vol, x, 1878, pp. 397, 398, 

 pi. Isii, figs. 4 a — e. 



This well-marked species and its varieties are widely distributed in the 

 Tertiaries of Europe. Especially in the Eocene at Woolwich and Newbury ; in 

 the Oligocene of the Isle of Wight ; and the Antwerp Crag. It occurs, with 

 the variety torosa, in myriads^ in the Hamstead Beds (especially the Lower beds), 

 tried by the boreholes of the Geological Survey in 1887. The trial-holes near 

 Newport and Gunville also found it in the Bembridge Marls. This species is 

 rarer in the Osborne series at Cliffend and in the Clay with oysters at Colwell Bay. 

 It occurs also in the Headon Beds and at Highcliff (F. E. Edwards). Recent 

 in the Zuyderzee (Bosquet), and " from Smyrna, the Levant, and Australia," 

 G. S. Brady, loa. cit. (Brit. Mus. and Mus. Pract. Geol.) 



3. Cytheridea montosa, sp. nov. Woodcut, Fig. 4. 



a b 



Pio. 4. — Cytheridea montosa, s'p. nov . a. Eight valve, h. Edge view, seen from the ventral margin. 



Magnified 20 diam. 



This small Gytheridea ("75 mm. long) is, at first sight, not unlike some 

 specimens of the var, torosa of G. Muelleri, but differs markedly in having, besides 

 a strong subcentral swelling, a thick, rounded, interrupted, and sausage-like ridge 

 nearly surrounding the surface, with numerous little shining tubercles scattered 

 over the rest of the valve. 



Rare in the Middle Hamstead Beds, Isle of Wight, at the Reservoir, half a mile 

 west of Medina Mills. (Museum Practical Geology.) 



' Figs. 9, 11, 12, illustrate species from the Isle of Wight, not from Woolwich. 

 - C. Muelleri inhabits fresh, brackish, and salt waters ; and is sometimes found in similar abundance 

 to that of these fossil multitudes. 



