218 WE8T AMERICAN SHELLS STEARNS. 



It is a small shell, the dimensions of the type, as stated by Carpenter, 

 being "long. .23, lat. .24," and the diameter or thickness .16 of an inch. 

 The shell is figured above for the first time. 



The varied and striking forms of the Carditidcc are conspicuously 

 represented on the western coasts of North and South America from 

 the subarctic waters of the Alaskan region as far to the south as Val- 

 paraiso in Chili. 



While some are globose and heart-shaped like the typical cockles 

 (Cardiura), others are exceedingly transversely elongated, and these 

 extremes are connected by intermediate forms. 



Of the cockle-shaped group, of which the commonly figured C. sul- 

 cata Lamarck may be regarded as an average illustration, we find the 

 following in the monographs credited to the Pacific shores of the two 

 continents : C. Cuvieri, the monarch of the group, with the varied and 

 peculiar C. Jlammea Mich., of which the G. varia and G. tumida of 

 Broderip are synonyms; G. crassa Gray and G. laticostata Sby, these 

 two rather intermediate and between the elevated umbonal and the 

 more elongate forms. While the extreme cockle-shaped forms in the 

 elevation and development of the umbones, as exhibited in large examples 

 of G. Jlamniea, approach Isocardia, yet the opposite extreme of trans- 

 verse elongation is gradually approached, and these two remote aspects 

 of shell characters connected, as may be seen when the general group 

 is reviewed as a whole. 



Following the more rotund, the suborbicular species of the Veneri- 

 cardia fall into place, represented by Conrad's borealis, Gould's ventri- 

 cosa, and my barbarensts, as above described, and certain small forms, 

 dwarfs or adolescents, perhaps extra-limital aspects of the several 

 facies of borealis figured and named by Reeve (Conch. Icon., PL ix) 

 as G. compressa, flabellum, and semen ; the first and second from Val- 

 paraiso, the third from the Bolivian coast, all small, insufficiently de- 

 scribed, and imperfectly figured. In addition to these is G. tegulata, a 

 small shell also in Reeve in the plate cited ; it is coarsely ribbed, and 

 in outline resembles ^a&eZ^?tw. Carpenter's j^roZow^/ato comes in here, 

 a little oblique shell with high umbones, and there are varieties of bore- 

 alis, small and semi globose, with granulose ribs. The granulation of 

 the ribs and elevation of umbones are varietal or local features, perhaps 

 both. G. borealis Conrad is figured here (Plate xvi, Fig. 8) for compari- 

 son with the other species above noted. 



The transverse shells of the group Garditamera (Conrad, lS3S=Laza- 

 ia Gray, 1853) includes the following : 



G. pectunculus Brug., 1790 ; G. affinis Sby., 1832 ; and G. califormca 

 Desh., 1852. The first has been credited to Madagascar,* no doubt 

 erroneously, and so far as I can learn said habitat has never been con- 

 firmed. A large example of G. californica which I have in my hand 

 at the moment of writing this, fits exactly to the figure in every way 



* Reeve's Conch. Icon, species 4, and Fig. 4, PL, 1. 



