94 R. BULLEN NEWTON on 



Family RAETOMYID^ (R. B. Newton, 1919). 



Genus Raetomya (R. B. Newton, 19 ig). 1 

 Proc. Mai. Soc. London, 1919, Vol. 13 pi. I, pp. 80-82. 



DESCRIPTION. Shell inequilateral, obliquely gibbose, thin, concentrically and 

 irregularly plicate, striated and wrinkled ; dorsal areas not defined ; anterior 

 side deep, long, oblique, depresso-concave, posterior region short, 2 marginally 

 compressed, reflected, slightly gaping ; umbonal areas arched, summits 

 opisthogyrous, incurved, oblique, laterally approximate but distant with age, 

 the right elevated above the left ; left valve with strong hinge-plate furnished 

 with a horizontally projecting triangular chondrophore marginally grooved 

 each side, deeply excavated anteriorly and striate within, succeeded by an 

 antero-marginal sulcus, the posterior side having a wider marginal sulcus to 

 receive the laminar tooth of the other valve ; right valve provided with a 

 shallow oval chrondrophore set back in the sub-umbonal cavity, obliquely 

 ridged posteriorly to connect with the postero-lateral groove of the left 

 chrondrophore, followed by a narrow sulcus, a posterior laminar tooth, and a 

 widely depressed dorsal furrow ; cardinal teeth absent in both valves ; pallial 

 impression widely indented by a nearly circular sinus ; adductor scars unequal, 

 posterior more or less normal, anterior narrow and elongate. 



TYPE. Lovellia schweinfurthi, Mayer-Eymar, from the Eocene (Upper 

 Mokattam Beds) of Egypt. 



REMARKS. This shell agrees with the mactroid genus Raeta? in most 

 external characters, but differs internally by possessing: (i) dissimilar 

 chondrophores, the left being triangular and projecting outwards, while the 

 right is triangularly ovate, vertical, and well within the sub-umbonal region ; 

 (2) no cardinal teeth ; (3) a large rounded pallial sinus. The chief external 

 distinction concerns the summits or umbones, which instead of being opposite 

 each other and nearly touching as in Raeta are laterally approximate but 

 becoming more or less distant with age, that of the right valve being always 



1 This descriptive account of Raetomya and of its species, R. schweinfurthi^ together with the plate of 

 illustrations (PI. io),have been reproduced from the original, published in the Proceedings of the Malacological 

 Society of London, 1919, Vol. 13, with the permission of the Council of that Society. 



2 In this respect resembling the genera Raeta, Nucula, Pisidium, etc. 



3 According to Dr. Ball the true systematic position of Raeta is still uncertain, since its soft parts 

 are unknown : Trans, Wagner Free Inst. Sci. Philadelphia, Vol. 3, pt. 4, 1898, p. 907. 



