332 FOSSIL OSTREID^ OF NORTH AMERICA. 



take place. After a few hours have elapsed, these embryos may be 

 poured into suitable inclosures, into which the sea- water may enter and 

 escape without carrying off the embryos themselves. In such inclosures 

 in which tiles coated with lime have been placed, it has already been 

 demonstrated that the embryos or fry will attach themselves to the tiles 

 and become transformed into young spat. As many as four thousand 

 have been found adherent to one tile, as a result of such experiments. 



During the present season the writer has successfully reared the spat 

 of the American oyster in a pond constructed ou the premises of Messrs. 

 Pierce and Shepard, near Stockton, Worcester County, Md. This pond 

 was dug out of a salt marsh; its depth was three feet and a half. It 

 was connected by a trench with Chincoteague Bay, adjoining. Into the 

 trench a wooden diaphragm was tightly fitted and filled with sharp 

 sand to filter the water passing into the inclosure, and to prevent the 

 escape of the artificially-fertilized embryos of our native species, which 

 were introduced into the pond at intervals during the month of July. 

 In forty-six days after the commencement of this experiment we found 

 spat measuring three-fourths of an inch in diameter attached to the old 

 shells which had been put into the pond to serve as collectors. This 

 experiment proves that artificial oyster culture is feasible in the United 

 States, and that marsh lands may become valuable where the adjacent 

 waters are of the proper density. 



The shells of the oyster are very irregular in form, in fact, scarcely 

 any two individuals ai'e to be found which are precisely alike. The 

 typical form of the shell of the American oyster is very well shown ou 

 Plates LXXVII and LXXVIII, and is iu fact the form most desirable in 

 the estimation of the grower and dealer. Other varietal forms are, 

 however, met with which diverge pretty widely from this one, as may be 

 inferred from the type represented iu Plate LXXIX, where the lower 

 valve is short and very deep. This second form is not a very usual one, 

 but aptly illustrates one of the extremes of variation of the species. 

 Another type now regarded as a variety of the common American oyster 

 is represented on Plate LXXX, and was formerly supposed to be a dis- 

 tinct species under the name of Ostrea borealis; the name having refer- 

 ence to its more northern habitat. Its most characteristic conchological 

 features are the deeply fluted valves; usually the lower one is the 

 most deeply fluted, while the upper one is nearly smooth, but sometimes 

 specimens are met with which have both valves very distinctly and 

 quite deeply fluted. Of this form Verrill remarks, " Even the same 

 specimen will often have the form of borealis in one stage of its growth, 

 and then will suddenly change to the Virginiana style, and perhaps, 

 later still, will return to the form of borealis. Or these different forms 

 may be assumed in reverse order." Lastly, a type of oyster is met 

 with in deep water or in crowded banks which has the valves abnormally 

 elongated as represented on Plates LXXXI and LXXXII, and known 

 as the raccoon or cat's-tongue oyster. This elongation of the valves 



