218 EDGAR A. SMITH. 



tratii, liiiins ; cardo edcntulus ; ligamentum intenmin in fossa 

 obliqua situin ; valvaB sutura oldiquaj rostrum prtDscribente, 

 inajqiialiter bipartita3. 



'riio principal distinguisliing features of this genus are the 

 joining of the valves along the dorsal, ventral, and anterior 

 margins, and their bisection by an oblique suture. The 

 ligament has a strong shelly support, and the outer edge of 

 it, near the umbo in the right valve, might be mistaken for 

 a cardinal tooth. The suture which bisects the valves is not 

 an accidental crack, as it occurs in all specimens, and marks 

 off the short rostrate posterior end of the valves. It even 

 bisects the umbones at their apices. The posterior adductor 

 scar is very strongly marked, deep, and the thickened edge, 

 which borders it on the anterior side, extends upwards, and 

 unites with the shelly support of the ligament. 



The form of the shell is very irregular, no two specimens 

 being alike. This would seem to indicate that the .species 

 lived in places inconsistent with regular growth, such as 

 crevices of rocks. This, however, is mere conjecture, and, 

 indeed, it might well be a parasitic form. 



Clistoconcha in sign is n. sp. PL YIII, figs. 9-9 c. 



Testa parva, tenuis, forma irregularis, subglobosa, postice 

 brevissime rostrata, hians, antice clausa, albida, vix pellucida ; 

 valvas tenues, subaequales, extra irregulares, striis incrementi 

 tenuissimis sculpta?, stria arcuata, ab umbonibus ad marginem 

 ventralein radianti et rostrum prajscribente, instructiv, ad mar- 

 ginem ventralem conjuncta? ; umbones parvi, in medio stria 

 radianti bipartite' ; pagina interna nitida, stria radianti con- 

 spicua bipartita ; cardo edentuliis; resilium obliquum })one 

 umbones, in fossa distincta situm ; cicatrix antica parva, 

 obscura, postica conspicua, profunda, irregulariter rotundata, 

 distincte circumscripta; linea pallii haud conspicua. 



Longit. 4'75, alt. 425, diam, 3 mm. 



Hab. — Tongaat, Natal (H. Burnup). 



The exterior of these curious shells is so irregular that at 

 a casual glance they have not the appearance of bivalves at 



