108 Mr. Gray on the Pidmonobranchous Mollusca. [Aug. 



Mollusca tracbelopoda, pallii niarginibus tenui- \ Lymnead e 



bus, testae labio sub uniplicato / 



Mollusca gasteropoda, pallio scuti-formi Onchidiad.k. 



The affinity between these families is so close that I shall not 

 have much difficulty in pointing out their connexion one with 

 another. Commencing with the Slugs ; they are connected with 

 the Snails by means of the genus Testacella, and indeed it is 

 exceedingly difficult to draw the line of demarcation between 

 the Limacida and the Helicida in the present imperfect state of 

 our knowledge with regard to the animals of the latter family. 

 But their shells may be known from those of all the other families 

 by their mouth being closed, when the animal is at rest, by a 

 peculiar membrane which is called an Epiphragma, or Poma. 

 The Snails are connected to the Auriculadce by means of a genus 

 named by Ferrussac, Partida, which has the eyes sessile, as in 

 the latter family, and also has the peculiarity of being ovo-vivi- 

 parous : therefore, we are thus led to the Auriculada, which 

 are mostly aquatic, or at least found in marshes. I should cer- 

 tainly exclude from this family the genera Pyramidella and 

 Tornatella, which Ferrussac has added to it, and place them in 

 the family Turbinidce, for the former has an operculum like the 

 Troc/ii, formed of many gradually enlarging, and the latter like 

 the Naticec, formed of a few rapidly increasing whorles, and they 

 both have the pectinobranchous animals of the latter group ; but 

 I would retain the genus Pedipes of Adanson, which is said to be 

 marine, in this family, on account of its near affinity to the Auri- 

 cula iiiteus of Lamarck (the Voluta triplicata of Donovan), 

 which, like several of this family, is found in salt marshes, or 

 estuaries, and I would also add to it the Voluta Jiuminea of Dr. 

 Maton, which, by the peculiar form of its outer lip, may perhaps 

 form a new genus. 



From this family, by the general similarity of the animals, the 

 general habitat, and particularly by the peculiar form of the shell 

 of Auricula Dombcyana, I proceed to the Lymncada', which are 

 all truly aquatic, and usually called Pond Snails, and which, by 

 the addition of the genus Phuiurhis to the divisions pointed out 

 by me in Sowerby's Genera, will form a very complete circle. 

 From thence, by means of the much shifted genus Ancylus, we 

 are led to the 0)ichidiad<c which only differ from them in being- 

 destitute of any shell ; and by means of the land section of this 

 family, which Ferrussac has placed with the Liuiacidcc, we are 

 led to return to that family, thus completing the circle, which, 

 at another opportunity, I shall attempt further to illustrate. 



It is impossible, till more is known of the animals of the Snails, 

 to point out distinctly the analogy between the genera of the 



