Zoological Society. 495 



ligamentary area, as to prevent the valves from opening beyond the 

 extent of about a quarter of an inch. 



Arca ambigua. Area testa subquadratd, tenuiculd, incequivalvi, la- 

 teribus subattenuato-angulatis, antico infra rotundato, postico an- 

 gulato ; albidd, epidermide fused, inter costas squamosa, indutd ; 

 radiatim costatd, costis tribus vel quatuor et triginta, angustis, 

 rotundatis, anticis subtilissime rotundatis ; ligamenti ared suban- 

 gust a. 



Conch. Icon. Arca, pi. 10. f. 65. 



Hab. ? 



"The Arca cistula is the nearest allied species to this. 



Arca cepoides. Arca testd subquadrato -ovatd, tenui, ventricosd, 

 incequivalvi, lateribus angulato-rotundatis ; albidd, fuscescente pal- 

 lida tinctd, corio corneo c&rulescente , epidermide fused, inter 

 costas squamosd, indutd; radiatim costatd, costis duabus et tri- 

 ginta, Icevibus, planulatis, costis valvce sinistralis sublatioribus ; 

 umbonibus tumidis ; ligamenti ared latiusculd, valde declivi. 



Conch. Icon. Arca, pi. 10. f. 66. 



Hab. San Miguel, South America (found in sandy mud) ; Cuming. 



This is a fine bold species, but it does not exhibit any very striking 

 peculiarity of character. 



Arca Hankeyana. Arca testd oblique ovatd, crassiusculd, valde 

 gibbosd, tumidd, cequivalvi, lateribus rotundatis, superne attenuatis, 

 latere antico brevissimo, postico oblique extenso ; albd, epidermide 

 tenui, inter costas hirsutd, sparsim indutd ; radiatim costatd, costis 

 duabus vel tribus et triginta, planulatis, confertis, quadriliratis ; 

 umbonibus parvis, distantibus ; ligamenti ared brevi, latd, declivi. 

 Conch. Icon. Arca, pi. 10. f. 68. 



Hab. Harbour of Mozambique (found in a mass of white coral on 

 the reefs at low water, spring tide) ; Hankey. 



I close this division of the genus with a new species, which ex- 

 hibits a peculiarity in the structure of the ribs of great novelty and 

 interest, each of them being composed of four distinctly separated 

 ridges. 



I have great pleasure in naming this important species after the 

 gentleman to whom I am indebted for it, Lieut. Hankey, R.N., a 

 zealous conchologist, whose researches on the coast of Africa have 

 greatly contributed to science. 



The following description of some new species of Columbella, in 

 the collection of H. Cuming, Esq., by Mr. G. B. Sowerby, was then 

 read : — 



Columbella Duclosiana, nob., Thes. Conch, part 4. pi. 36. f. 15, 

 16. Col. testd ovatd, utrinque acuminatd, longitudinaliter costel- 

 latd, saturate fused, zonis bints pallidioribus ; spird acuminatd, 

 anfractibus 5, costatis, ultimd magnd parte ventrali longitudinaliter 

 costatd, interstitiis costarum transversim striatis, dorsali Icevigatd, 

 antice transversim striata; aperturd latiusculd, fiexuosd, nigri- 

 cante; labio externo crasso, intils denticulis 8-9, posticis majori- 



