44 



THE NAUTILUS. 



'/raitum; but besides certain differences in form, this has an Ainni- 

 coloid operculum, while in yrnmnn it is Valvatoid. 



The specimens from River Rouge are smaller and more elongated 

 than average shells of the type lot ; those from Reed's Lake are 

 fairly typical in form, but perhaps a little thinner. 



The name is in honor of Mr. Bryant Walker, to whose acumen 

 the discovery of the form, and of its distinctness from known Michi- 

 gan Amnicolidse, is due. 



While investigating the characters of the above species, I have 

 had an opportunity, through the courtesy of Prof. W. H. Dall, to 

 examine the types of Amnicola parva and A. orbiculata Lea, de- 

 scribed from Springfield, Ohio. 



A. parva is like A. limosa in the umbilicus and obtuse apex, but 

 is smaller with the whorls particularly tumid just below the suture, 

 producing a somewhat shouldered appearance, such as characterizes 

 Amnicola cincinnatiensis (Anth.). The same form occurs at Joliet, 

 Illinois, Muscatine, Iowa, etc. It measures alt. 3'8, diam. 3'2 mm. 

 or somewhat smaller. Whether it is a stunted form of limosa due 

 to unfavorable station, or is constantly distinguishable I have not 

 ascertained ; but it is at all events quite recognizable. The types 

 show more or less blackish incrustation about the spire, and evidently 

 did not occur with Lea's specimens of orbiculata. 



A. orbiculata is absolutely identical with A. limosa var. porata 

 Say. The specimens vary between the widely umbilicated porata 

 form, and an intermediate form. They are finely grown shells, quite 

 fresh though without opercula, and rather corneous than " yellow- 

 ish " as Lea says. There was no " mistake " about Lea's "specimen 

 of this species among many small shells which were thrown together 

 in a box, as being collected from our vicinity " (Philadelphia), for 

 Hinosa and porata are abundant in both the Delaware and Schuylkill 

 rivers. Two of Lea's type lot measure : 



Alt. 5, diam. 4 mm. 



Alt. 4, diam. 4 mm. 



A NEW SPECIES OF TEREBRA FROM TEXAS. 



BY W. H. DALL. 



Some years ago the Hon. J. D. Mitchell, of Victoria, Texas, sent 

 to the National Museum a much dilapidated specimen of Terebra 



