96 R. BULLEN NEWTON on 



Raetomya schweinfurthi (Mayer-Eymar). 



PLATE 10. 

 Lovellia schweinfurthi. 



Mayer-Eymar: Journ. Conchyl. 1887, Ser. 3, Vol. 27, pp. 320-322, pi. II, fig. 6. 



Raeta schweinfurthi. 



Oppenheim : Palaeontographica, 1906, Vol. 30, part 3, pp. 190, 191, pi. 19, fig. i, text figure 17. 



Raetomya schweinfurthi. 



R. B. Newton : Proc. Mai. Soc. London, 1919, Vol. 13, pp. 79-84, pi. i. 



REMARKS. The Nigerian specimens referred to this species, hitherto only 

 known from the Egyptian Eocene, vary considerably in size, the smallest 

 showing a length and height respectively of 25 and 20 mm., while one of 

 maximum size, a natural cast with united and closed valves, measures 1 1 3 by 

 75 mm. ; the dimensions of the type being 65 by 54 mm. 



The chief features of interest of this Pelecypod are the very inaequilateral 

 and obliquely gibbose valves ; the thin test with its sculpture of more or less 

 regular concentric ridges ; the narrow, elevated umbonal regions and their 

 laterally approximate incurved beaks ; the possession of an elongate, depressed, 

 anterior end region, slightly concave above and rounded at extremity, while 

 the posterior side is short, wide, marginally compressed, reflected, and slightly 

 gaping ; pallial sinus widely arcuate ; hinge-plate small with an anterior 

 lamellar tooth parallel to the margin, as well as an oblique and strongly 

 lamellar posterior tooth ; no cardinal teeth referred to. These characters, 

 mostly mentioned in the original account, are mainly of external interest, very 

 little apparently being known as to those affecting the interior of the valves. 

 The new and better preserved material from Southern Nigeria fortunately 

 supplies some important details of internal structure which contribute to the 

 value of the species, as well as suggesting its recognition as the type of a 

 new genus ; the emended specific characters may be set out as follows : 



Umbonal region well elevated and arched ; summits resting on the shell 

 margin, opisthogyrous, laterally approximate but divided in age, that of the right 

 valve always slightly raised above the other. Left valve with a strong hinge- 

 plate, having all its elements coalescent and radiating from beneath the umbonal 

 region, which embrace : a horizontally projecting chondrophore of elongate 

 triangular shape and slightly concave surface, bordered by a posterior groove, and 

 followed by a steep, oblique, posterior side which forms part of a wide and deep 



