OF MOLLTJSCA. 



65 



a long time out of water when the marshes dry up. They afford 

 nourishment to the marsh birds, especially the large Kails. 



§ Siphon not produced. Operculum horny, with shell]/ internal 

 coat. Peristome thickened. 



1. Pachystoma. 

 Shell subglobose ; spire short. Peristome continuous, thickened 

 on the edge within ; nucleus subcentral. Operculum horny, with a 

 shelly internal coat. — Adams, Gen. Moll. t. 37. f. 1 a, b. 



1. P. fasciata, t. 47. f. 3 ; Adams, Gen. Moll. t. 37- f. 1. 



2. P. Cebensis, t. 47. f. 1, 2 & 4. 



2. AsOLENE. 



Shell subglobose ; spire short ; aperture oval ; inner lip slightly 

 thickened ; outer thin ? Operculum horny, with an internal shelly 

 coat ; nucleus lateral, anterior ; siphon not exposed. 



1. A. Platae, t. 47*. f. 4. 



Asolene Plata is found in small marshes on the sands near the 

 La Plata, at the roots of water plants ; its movements are very slow, 

 and it seldom comes out of its shell. 



m 



§§ Siphon of mantle elongate, produced. Operculum horny, simple. 

 Peristome thin. 



3. Marisa. 



Shell discoidal, largely umbilicated. Peristome simple. Oper- 

 culum horny {Adams, Gen. Moll. t. 37. f. 3). Siphon elongate. 



1. M. cornu-arietis. Ampullaria c, Lamk. ; Adams, Gen. Moll. 

 t. 37. f. 3. 



4. Ampullaria. 



Shell subglobose, perforated; mouth large. Peristome simple, 

 thin. Operculum horny, dextral (Adams, Gen. Moll. f. 2 a, b) 

 (fig. 35). Siphon elongate. 



1. A. zonata, t. 47*. (.2. Fig. 35.— Operculum of 



2. A. Rossii, t. 47*. f. 1. Ampullaria. 



3. A. scalaris, t. 47**. f. 2 ; Adams, Gen. Moll. 



t. 37. f. 2. 



4. A. Ureus, Troschel, Wiegm. Arch. 1845, 197. 



t. 8 (anat. f. 3, teeth). 



5. A. canaliculata, t. 47**. f. 1. 



6. A. insularum, t. 117. f. 1. 



7. A. , t. 117. f. 2. 



Lingual membrane of Ampullaria ? linear elongate. Teeth 



3 ■ 1 • 3 ; central broad, short ; apex slightly recurved, with a strong 

 central tooth and a small toothlet on each side ; inner lateral tooth 



