- 172 - 



;^emar''S .- This species is desoribecl from two fragments, 

 fae median portion of a rirht valve and an immature, almost oom.- 

 plete left valve with the er-ctreme posterior re2;ion lacking. On 

 the larp-er fragm.ent most of the posterior muscle scar is visible, 

 showing that it is large, longitudinally elongate, converly round- 

 ed posteriori;/, ventral in position. The principal features are 

 the strong, asymmetrical converity, prominent e temal sulcus and 

 the character of the sculpture. 



The Oaloosahatchie P. caloosagnsis Dall (1) is heavier, more 



(1). Trans. Wagner Free Inst. Sci., Philadelphia, vol. Z, -ot. 4, 

 p. 550, pi. 26, fig. 4, 18X1. 



symmetrical, v/ith a broader, higher internal ridge and different 

 sculptiire. P. rudis (Linnaeus) Dillwyn (2), a recenl; West Indian 



(2). Linnaeus, Syst. Kat., ed. 12, no. 1159, 1766, e:c parte; 

 Dillwyn, 'Jat. Rec. Shells, p. 522, 1817; Reeve, Conch. 

 Icon., Pinna, "ol. 10, fig, 19, 1858. 



species, is thinner, with a less conspicuous external sulcus 

 and internal ridge and differs also in sculpture; the other 

 recent '.Vest Indian form, P. carnea C-melin f^l, differs in a simi- 



iZ). Syst. llat., p. 3565, 1792; Reeve, Gonch. Icon., -inna . 

 pi. 20, fig. 18, 1858 (as P. flahellun) ) . 



