48 n 



A MANUAL OF AMERICAN LAND SHELLS 



overlapping the peristome of the shell, and bilobed; respiratory and 

 aual orifices iiuder the peristome ; orifice of generative orgaus behind 

 the right eye peduncle ; no caudal mucus pore; no locomotive disk. 

 Shell imperforate, ovate or oblong-conic, thin, striated, decussated 



Fig. 480. 



Animal of O. undatus. 



with curling lines, and ornamented with usually articulated fillets and 

 oblique swaths; whorls 6-8, the last inflated; columella filiform, loosely 

 arcuated intorted, obliquely subtruncated at base; aperture oval; 

 peristome straight, its margins connected by a light callus. 



The jaw of the only species within our limits, 0. itnclatusj Brug. (see 

 Fig, -481), is of the type usual in this genus and Ligims (see above), but 

 up to the present time never observed in any other genus. It is com- 

 l)osife, its separate pieces being ai)parently soldered firmly at their 

 upper portions, where, indeed, they seem collectively to form a jaw in a 

 single piece, as in Patula, «&c., but at their lower portion positively de- 

 tached and free, imbricated one upon another. The jaw may in one 

 sense be said to be in a single piece, as -argued recently by Messrs. 

 Fig. 481. Fischer and Crosse (Moll. Mex. et Gnat.), 



but with equal correctness it may surely 

 be said to be composite, as the amalga- 

 mation of the upper j)ortion is produced 

 by the joining of absolutely separate 

 Jaw of o. undaHis. picccs. There are seventeen of these 



plates in the jaw figured, though the number varies, the upper central 

 one apparently lying upon the adjoining ones, which are broad and ex- 

 tend from the upper to the lower margin of the jaw. The jaw is 

 strongly arched, with attenuated, blunt ends. There are well-marked 

 perpendicular grooves upon the anterior surface of many of the plates. 

 The upper central plate is triangular, from which fact the name Goniog- 

 natha has been applied to the section. Cylindrella, Ifacroceramus, 



