"SLIPPEB LIMPET'' OB ''BOAT SHELL:' 403 



market for the Whelk-Tingle, which in Oyster-culling is either 

 thrown anywhere overboard, or at sparse times is crushed under 

 foot on deck, but seldom or ever collected and taken ashore to 

 be destroyed for the ultimate benefit of the Oyster-bed. 



Its ally, the Common Whelk {Buccinum undatum), some aver, 

 has an occasional turn at the Oyster, but the injury they commit 

 is slight compared with the Tingle. Besides, there is a regular 

 fishery — ** Whelk Trotting" — existent in the Thames estuary 

 and Harwich neighbourhood. The catch therefrom as a con- 

 stant trade is either sent to market and sold as food, or de- 

 spatched to the North Sea trawlers as bait. Other enemies we 

 leave aside as apart from the object at present in view. 



"Slipper Limpet" or "Boat Shell" {Crepidula fornicata) . 



This Gastropod, as already intimated, is an American form 

 of but quite recent acquisition among the British marine fauna. 

 Its distribution in the North American continent is the Atlantic 

 Coast from the Maritime Canadian Provinces along the United 

 States shores to Florida and north of the Gulf of Mexico. 



Although in the colloquial the animal is named " Limpet," 

 yet it differs structurally in the soft parts, and the shell does 

 not possess the conical form of our Common Eock Limpet 

 (Patella vulgata). Thus it comes under another genus — Crepi- 

 dula. Instead of a Limpet's figure, the shell is ovoid or oblong 

 in shape, with a curled or twisted beak. 



In our British specimens it may range from one-eighth of an 

 inch to nigh 2^ in. in long diameter, and in breadth from | in. 

 to 11 in. in greatest width. The height varies -^q in. to 1^ in., 

 according to the different age and stage of the animal when 

 alive. Much or nearly all depends, however, whether the shell 

 is flattish or more arched on the top curve, and this varies to a 

 remarkable degree, according to the contour of the object to 

 which it is adherent. 



A remarkable feature of the shell, and that which has given 

 rise in the United States to the names of " Slipper Shell " and 

 *' Boat Shell," is the presence of a horizontal thin plate of 

 porcelain-like nacreous material. This separates the powerful 

 muscular foot from the softer viscera, which lie ensconced safely 

 and securely above. Compare in Plate VI., figs. 7 and 8, where 



2i2 



