98 MONOGRAPH OF THE GENUS GNATHODON—DALL. vol. xvii. 



ceivedfroin Mr. J. D. Mitchell, of Texas, a living specimen upon which 

 an oyster, at least two years old, and several specimens of Mytilus 

 hamatus were tirnily attached. 



Details in regard to this species will be found under the discussion 

 of the genus. lam informed that on the Texas coast it has been 

 extensively preserved for food in cans under the name of "Little Neck 

 Clams," and has met with some favor, gastronomically. 



The dimensions of an adult specimen are as follows: Length 75, 

 height GO, diameter 50 mm.; but the proportions vary somewhat Avith 

 the amount of rostration of the individual. 



The epidermis of G. cuneatns is normally of an ashy gray color, some- 

 times with a tinge of greenish or brownish, and of a papery consistency. 

 When worn it has a more brownish tint, and some specimens display 

 streaks of a light ferruginous brown when the epidermis is thick and 

 worn. There is sometimes shown a smoother and more translucent 

 area of epidermis in the region where the lunule and escutcheon of 

 bivalves usually occur, though these areas are not set off by any groove; 

 but they are chiefly visible in adolescent specimens and often absent 

 entirely. Toward the posterior end of the shell the epidermis is often 

 raised in fine wrinkles, and it is usually more or less eroded on the 

 beaks. The sculptnre of the exterior of the valves is chiefly incre- 

 mental and irregular, but many specimens show traces of radiating 

 raised threads, especially in the rostral region. A wide obscure 

 depression extending from the beaks to the margin and, with the valves 

 closed, circumscribing a cordate area, is visible on the anterior end of 

 many specimens. It corresponds nearly to the lower i)art of the 

 anterior adductor scars within the valves. No umbonal sculpture like 

 that of many unios can be observed on the uneroded beaks. They 

 are always smooth, as in Mactra. 



In common with most brackish water shells this species has a con- 

 siderable range of variability in form. In this case it chiefly arises 

 from a difference in the height of the umbones, and especially from the 

 shape of the posterior extreme of the shell, which normally is somewhat 

 produced and evenly rounded at the margin, but in other cases is 

 somewhat rostrated, with the basal margin somewhat concavely flex- 

 uous. This is carried to an extreme in ji variety which may be called. 



GNATHODON CUNEATUS xnv. NASUTUS, Dali. 

 Plate VII, fig. 8. 



In salt water at Port Lavaca, Texas, Mitchell. 



Length 35, height 27, diameter 24 mm,, in the typical specimen. 

 This form was foiind by Mr. Mitchell, with others of the typical char- 

 acter, in pure salt water on the Texas coast. The specimen is small 

 compared with the adult of the type form, but seems mature and is 

 quite thick. It has nearly the form of G. Jiexuosus, but can at once be 



