458 BULLION. 



shaped, lying at the base between the two lateral plates ; each 

 plate has two small holes (muscular impressions?) in the 

 middle : odontophore, rhachis wanting ; uncini 12-15, arranged 

 in a single row, claw-shaped, and furnished on the inner side 

 with a jagged crest. 



SHELL squarish oval, depressed in front, very thin and fra- 

 gile, semitransparent, glossy, and iridescent : sculpture, plait- 

 like and irregular lines of growth, and a few extremely slight 

 and more irregular spiral lines, which latter are not discern- 

 ible except with a lens and at certain angles of light; the 

 texture, examined under a microscope, resembles curdled milk : 

 colour whitish, with sometimes two or three clear streaks across 

 the back : spire very loosely coiled, with the nucleus extremely 

 small and concealed by a shelly deposit from the hinder lobe 

 of the mantle ; it is always more or less indented, and in the 

 young is slightly umbilicate : mouth roundish-oval, of enor- 

 mous size compared with that of the convoluted portion, and 

 occupying seven-eighths of the under surface ; it is obliquely 

 truncated above, and rounded below : outer lip dilated, with 

 a sinuous and very thin edge ; the upper part slopes outwards, 

 and projects considerably beyond the spire ; inner corner re- 

 ceding and acute-angled : inner lip spread over the pillar, and 

 forming at the angle where it meets the outer lip a thick and 

 shapeless callus : pillar sharp and flexuous ; there is no um- 

 bilical groove or depression. L. 0-85. B. 0*7. 



^I&T. patula. Smaller, with the mouth larger and more 

 expanded. 



HABITAT : Sand, from low-water mark of spring tides 

 to 50 f., on all our coasts between the Firth of Forth 

 (Forbes) and Jersey (Dodd). It seems to attain its 

 largest dimensions in the Bristol Channel ; specimens 

 which I found in Swansea Bay are nearly an inch and 

 a quarter in length. The variety is from Tenby, Dub- 

 lin Bay, and Connemara. I am not aware that this 

 species has occurred in a fossil state except at Belfast, 

 where Mr. Grainger observed it. Its existing distri- 

 bution comprises the Atlantic sea-board from Upper 

 Norway to the Canaries, the Mediterranean, Adriatic, 

 and ^Egean, at depths varying from 4 to 110 f. ; sped- 



