P L E I D N . 



Genus PLEIODON, Conrad. 

 Tesla JluviatUk, aqidculcis, hi,r<jiiiJnkraUs, ovalis, iidiis 

 margaritacm, iwliis c]itili'r.,iiili' crassd laivigald iii- 

 duta, margine cardiiiidi i-iiinplcniato, erasso, tubercidis 

 ohlongh trauwemia irregularibun crenato. 

 Sliell fluviatile, equivalve, inequilateral, oval, pearly insiili', 

 covered with a smooth, thick epiderniis outside, 

 hinge margin flattened, thick, crenated with oblong, 

 transverse, irregular tubercles. 

 Only two species are known of this genus, both from 

 C'eutr:d Africa. Both species are thick shells, of au ovate 

 form, witli broad, laminar, wrinkled hinges. The species 

 of li-idiiia, on the contrary, arc thin, long, straight shells, 

 with linear hinge not always crenated. 



Pi. 1.1 



Species 1. (Mus. Sowerby.) 

 ov.\TUS. P. iesta ohUque ovatd, tumida, m- 

 ttis murgaritaced, roseo-argeiifed, extus epidermide o/i- 

 vaced, latere a?iUco breviusculo, ang/tsio, medio iiijlaio, 

 lalo, latere postko suharignlato, oblique truncato, mar- 

 giric dursali elevalo, margine cnrdiiiali lato, postici 

 truncato, angiilatini. crenato, medio contructo, antice 

 brevi subradiatim crenato. 

 The ovate Pleiodon. Shell obliquely ovate, tumid, 

 pearly, rose-silvery within, with an olive epidermis 

 without, anterior side rather short, narrow, middle 

 inflated, broad, posterior side rather angular, ob- 

 liquely truncated, with dorsal margin elevated, hinge 

 margin broad, posteriorly truncated, angularly cre- 

 nated, in the middle contracted, anteriorly short, 

 subradiately crenated. 



Sw-.UXSON, Zoological lllnstra 

 Pleiodon M-.Mnrtrei, L'oui 

 Ilnb. Central Africa. 



one 



L- niost bi'autlful shells of the whole 

 Mussels." 



Species 3. fMus. Brit.) 



Pleiodon Speicii. 7-'. tesfd oblongd, tnmidd, intns sub- 

 riifd et argenteo-cftrided, extns epiderniide castaned, 

 versns mart/inem ventraieni nigrescente, latere antieo 

 brevissimo, angnsto, medio ad viarginem rentraleni con- 

 tracto, latere politico ehmgato, oblique snbtruiicato, ter- 

 inine acuminato, margine dorsali elecaio, margine car- 

 dinali infra itmbonem emarginato, antice brevissimo, 

 leei.ter crenulato,postice elongato snbradiatim crenato. 



Speke's Pleiodon. Shell oblong, tumid, within rather 

 rufous and silvery-blue, without with a chestnut epi- 

 dermis, beeoniing blackiih towards the ventral mar- 

 gin, anterior side very short, narrow, middle con- 

 tracted at the ventral margin, posterior side elon- 

 gated, obliquely subtruncated, extremity acuminated, 

 dorsal margin elevated, hinge margin emarginate 

 under the umbo, anteriorly very short, slightly cre- 

 nulatcd, posteriorly elongated, subradiately crenated. 



WoODWAiiD, Pro. Zool. Soc. iSS'J. 



Hub. Lake Tanganyka, Central Africa. 



The unique specimen in the Britisli ^Museum was 

 brought from the great freshwater lake by the African 

 traveller whose name it bears. 



August, 18CG. 



