74 THE NAUTILUS. 



borrowers retire is a comparatively thin coating over a stony or 

 rocky layer which they cannot pierce, the tendency in Panopea, 

 Mya, etc., is for relatively short and broad shells, with shorter 

 siphons, to survive ; which naturally have a wider, shorter, and more 

 rounded pallial sinus, and shorter and more incurved nymphs. I 

 believe the influence of environment is direct and not selective ; at 

 all events the association of situs and specimens so characterized is, 

 as far as I have been able to determine, quite uniform, whether 

 selective or not." 



While living at St. Augustine, Florida (1880-87), I was fortu- 

 nate in finding in the harbor, on a sand; bar near " Marsh Island," 

 a specimen of Panopea bitruncata with valves intaot. and from which 

 the animal had apparently just been removed. This specimen which 

 is shown on plate IV, represents a nearly normal shell (reduced ;il>out 

 one-fifth) with the lines of growth but slightly interrupted anteriorly. 

 It had probably grown under favorable conditions in the adjacent 

 sandy-mud bottom. The shell measures 133 mm. (o.25 inches) in 

 length, with a width of 80 mm. On the ocean beach I also found 

 several single valves; these were proportionately shorter, and wider, 

 giving them a more truncated appearance. In my list of the slidU 

 of St. Augustine, Florida, in this Journal, Volume IV, page 4, 1 re- 

 ferred these to Glycimeris bitruncata Conr., while in naming the one 

 from the harbor, I followed Dr. Dall's catalogue of the shell-bearing 

 mollusks of the southeastern coast of the United States (Bull. 37, 

 U. S. Nat. Mus.) and called it G. reflexa Say. 



Since Dr. Dall's review of the species (Trans. Wagner Free lust. 

 Sci. Vol. Ill, pi. 4, p. 831), I have made a careful study of the type 

 of P. bitruncata in connection with all recent specimens obtainable 

 and find no greater variation than exists in the Pliocene specimens of 

 Florida. The type of P. bitruncata is an injured specimen ; the 

 upper or dorsal portion of the posterior end being broken away, 

 gives the shell a very oblique truncation, while the lower portion of 

 the anterior has been frequently arrested in its development, the 

 lines of growth being interrupted and crowded together, gives that 

 end also a very oblique outline. The umbonal and younger portion 

 of the shells are alike in all the specimens I have examined. 



Uniting the recent and Pliocene forms, and adopting the oldest 

 name will make the synonomy stand as follows : 



