MOLLUSCA. 513 



mai-gin marked by an impressed line between the valves. Sur- 

 face of the shell, which is rarely preserved, marked by lamellose, 

 concentric lines of growth. 



Remarks. — ^This species occurs most frequently in the Nave- 

 sink marl, where it attains its maximum size, but one colony 

 of shells has been detected in the recent Survey collections from 

 the Wenonah sand, the individuals of which seem not tO' differ 

 from those in the Navesink, except that none of them exceed 

 10 mm. in length. In connection with his original description, 

 Gabb mentions having collected one specimen oif the species from' 

 near the place now known as Westville, the horizon of which 

 would be Merchantville clay-marl, but the species has not been 

 detected in the recent collections of the Survey from this horizon. 

 Gabb's two' species, ripleyana and affinis, are undoubtedly not 

 distinct, and are here united under the one name ripleyana. 

 Gabb himself recognized the identity of the twO' forms in his 

 later notes on the species in 1876, but Whitfield has recognized 

 both forms. Among such burrowing and attached shells it is 

 necessary to allow a far greater range of variation than in most 

 others. These shells burrow into various substances, usually 

 wood, but Whitfield mentions finding them in the shell of Ger- 

 villopsis ensiformiSj and they have been observed by the writer 

 burrowing in the shells of Gryphaea vesicularis at MuUica Hill. 

 Formation and locality. — Merchantville clay-marl, near West- 

 ville (Gabb); Wenonah sand, near Crawfords Corner (126^); 

 Navesink marl, 'Marlboro (131), Crosswicks Creek (195), near 

 Walnford (148^), Mullica Hill (169). 

 Geographic distribution. — New Jersey. 



Order ANOMALODESMACEA. 



Super-family ANATINACEA. 



Family PHOLADOMYAOIDAB. 



Genus PHOiyADOMYA Sowerby. 



Pholadomya occidentalis Morton. 



Plate LVI., Figs. 1-3. 



1833. Pholadomya occidentalis Mort., Am. Jour. Sci., ist ser., 



vol. 23, p. 292, pi. 8, fig. 3. 



33 PAL 



