NEiERA. 199 



N. cosTELLATA, Deshajes. 



Small, white, beak produced, surface more or less sculptured 

 with radiating costell?e. 



Plate VII. figs. 8, 9 (the smaller figures represent tte natural size), and (animal) 

 Plate G, figs. 8, 9. 



Corkda costellatafDESH. Exped. Scient. Moree, MoUusques, p. RG, pi. 24, f. 1, 



2,3. 

 NecBi-a costellafa. Hinds, Proc. Zoolog. Soc. 1843, p. 77. — Jeffreys, Ann. Nat. 

 Hist. July, 1847, p. 19. 

 „ sulcata, LovEN, Index Mollus. Sueciae, p. 48. 



The outline of this extremely rare and recent addition 

 to our Fauna, is rather obliquely pear-shaped, the resem- 

 blance to the contour of that fruit not being disturbed 

 as in cuspidata, by any projection of the umbones. The 

 valves are much less inflated than in the other two sjiecies, 

 being but moderately ventricose. The epidermis which, 

 however, is rarely preserved, aj^pears when present to be of 

 a pale-ash colour, becoming olivaceous towards the lower 

 margin ; the shell itself is white, thin, fragile, and very 

 nearly equilateral ; and is adorned with a very variable 

 number of radiating linear ribs, which, commencing ante- 

 riorly to the concavity which precedes the rostrum, di- 

 minish in elevation, and become more approximate to each 

 other as they recede from that part, either disappearing or 

 changing into mere radiating lines near the anterior extre- 

 mity, and upon the front umbonal region. The actual 

 costellse (not the radiating lines), seem to be fewer on the 

 right or larger valve, than on the other one. The ventral 

 margin is moderately subarcuated, the chief swell being 

 near the anterior extremity ; it rises posteriorly and, form- 

 ing a rather profound sinus on arriving at the very oblique 

 linear rib, which is the hindmost of the series of costella?, 



