34 PROCEEDINGS OP THE ACADEMY OF 



II. Rostrum produced, extending into two much elon- 

 gated, subulate lobes Ampcllariid^:. 



AA. Gills pinnate, plumose and exsertile forwards Valvatid^. 



II. Teeth of lingual membrane x | 4.1.4 | x; central very 



unequal: lateral slender, hooked and very numerous... Rhipidoglossa. 

 Shell with a straight, flattened columella Neritid^:. 



Size, in the several families above enumerated, is, as a rule, correlative with 

 structure. The Ampullariidx are comparatively large ; the Viviparidm moder- 

 ate ; the Melaniidze smaller, and the Valvatidse and Amnicolidse generally may be 

 almost said to be minute. 



The family of MelaniiDjE is here restricted to exclude Faunus Montfort, 

 ( =Pircna Lam.), Melanatria Bowdich, Melatoma Sw., (= Clionella Gray,) 

 Melanopsis Lam., Vibez Oken and Hemisinus Sw. These appear to belong 

 to a distinct family equally distinguished by the projecting foot of the 

 animal and the notch of the aperture of its shell. The family may be named 

 Melanopid.. The other genera or subgenera that have been proposed scarcely 

 appear to exist in nature. There is, however, one form which has received no 

 name ; it embraces the species figured by Chenu, under the names of Melanopsis 

 princeps (Lea) and M. acicularis Ferussac. This genus is most nearly allied to 

 Faunus, with which it agrees in physiognomy, but is distinguished by the ab- 

 sence of a posterior sinus of the outer lip ; it may be named Faunopsis.* The 

 American Melaniidse form a peculiar subfamily, Ceraphasiinse. 



The Amnicolims of North America may be distributed among two subfami- 

 lies, Amnicoliw-e and Bythinin^e. The Amnicolinse represent, apparently, 

 three genera, Amnicola ; Chilocyclusf (Gill), with the circular lip reflected, 

 and with a shell like Amnicola, and Somatogyrus ; (n. g.) J with the body 

 whorl globose, and the aperture obliquely semicircular. The validity of Ponia- 

 tiopsis, as defined by Tryon, is for me very doubtful. 



The Ampullariidse are represented by the genus Ampullaria Lam. 



The Valvatidse are divisible among two genera Valvata, from which Tropidina 

 is apparently not separable, and Lyogyrus, (n. g.) in which the last whorl is 

 separated from the preceding and revolves within the normal spiral of in- 

 crease. 



The families of Viviparidse and Amnicolidse may be further distinguished by 

 the following characters, which are essentially the same as those used by M. 

 Moquin-Tandon to distinguish the so-called "genera" Faludina and Bythinia. 

 The contrast is made simply because the genera have been confounded under 

 one family, for they are really less related to each other than Bythinia is to the 

 Melanians, or some other families. 



Family VIVIPARIDSE (Gray,) Gill. 



Animal oval, entirely retractile within the shell. Foot oval, much dilated, 

 passing beyond the muzzle, and provided with an anterior groove. Jaws two, 



t 



Faunopsis (Faunus, mythological name and O-^i;,) Melanopince. Testa elongata, 

 subulata, apertura parva, rhombo-ovata,postice acuta, antice bene sinuata, labro externo 

 acuto, nee sinuata. 



Type. Melanopsis princeps Lea. 



tChilocyclus (Xmxoc, lip, and Kc/xaoc, circle.) Testa conica,anfractibus con vexir, 

 apertura modica, circulari, labro reflexo. 



Type. Cyclostoma cincinnatensis Lea. 



I Somatogyrus (Sa^a-roc, body and Tupo;, whorl.) Testa anfr. primo globoso, spira 

 parva, apertura obliquiter semi-circulari, labro externo acuto. 



Type. Amnicola depressa Tryon. 



(j Lyogryrus (m/o> to loose and yvpos, whorl.) Testa, oblonga, anfr. convexis. anfr. 

 ultimo disjuncto, apertura circulari. 



Type. Valvata pupoidea Gould. 



[Feb. 



