124 THE PROCEEDINGS OF THE LINNEAN SOCIETY 



confluentibus ; rostro compresso, rotundato, vix recurvo, a margins 

 postico sinu lato, angulato, sejuncto, superne ab umbonibus irregular- 

 iter crebre transversim corrugaio ; lunula lo?iga, angusta, lanceolata, 

 parum impressa ; umbonibus parvis, incurvatis ; pagina interna 

 lactea, nitente corrugata ; impres. muse, magnis sat conspicuis ; fossa 

 ligamenti, cochleariformi, prominenti. Long, 13, Lat. 22, alt. 9, 

 long. rost. 7, lat. (circiter) 4, mill. 



Shell fragile, oval, ventricose, anteriorly wider, rounded, 



obtusely angular ; posterior with a long rostrum ; milky white, 



opaque, concentrically sulcate and plicate, plaits 12 to 16, broad, 



flattened, angular above and subacute, becoming wider with age, 



rolonged upon the rostrum, deflected by a posterior sinus, then 



lightly curved, and often confluent ; rostrum compressed, 



Dunded, slightly re-curved, separated by a wide angular sinus, 



the upper part closely transversely corrugate from the umbones 



to the end ; lunule long, narrow, lanceolate, slightly impressed ; 



umbones small, incurved ; interior dull milky white, shining, 



corrugate ; muscular impressions large, rather conspicuous, 



ligamental fossa spoon -shaped and prominent. 



This singular species is mainly remarkable for its broad 

 corrugations, which show inside the valves, and for the singular 

 sinus at the rostrum, where the plaits become straightened out, 

 and either parallel or confluent, following the marginal side of 

 the prolongation on whose upper side, fine striae (which continue 

 to the umbone) are given off at right angles to the axis. 

 These striae seem to agglutinate to themselves fine particles of 

 sand, &c. The shell is somewhat like the British N. cuspidata, 

 Olivi, bat differs in the corrugations, the peculiar marks on the 

 rostrum and the sinus, which in the species referred to is double. 

 Theora fragilis has no proper rostrum, and is pellucid. N. rugata 

 is finely striate on both rostrum and shell. There are some 

 mesozoic fossil forms somewhat like the new species. Necera is 

 a genus which has been existing from the Oolitic period, since 

 when it has been gradually increasing in number. 



