On the Morphology of the Organs called Lenticels. 273 



racter of Truncatella applies to only one species, and is therefore 

 partial, untenable, and contrary to authorities. 



AVe now eome to a later epoch, when malacology has fur- 

 nished an essential generic character for Truncatella which no 

 other British mollusk has yet been found to possess, that is, 

 the immersion of the eyes in the tissue (instead of being placed 

 on pedicles as is usually stated) at the sviperior and nearly ter- 

 minal points of the short, strong, divergent, almost rectangular 

 tentacula : this structure stamps the so-called A. Grayana a 

 Truncatella, and is that of every other British species of the 

 genus. 



Dr. Gray then terminates his reasoning with a malacological 

 observation, that I have described the Truncatellce of my work 

 on the British Marine Testaceous Mollusca as having a white 

 iris (? pupil), and that I had not observed in A. Grayana a 

 similar appearance, on which account he seems to throw a doubt 

 of its being a Truncatella. I do not understand the logic of 

 this ; the point in question is a mere specialty ; one may with as 

 much reason say that a man with a red iris or pupil, for example 

 an albino, is not of the genus Man, because he has not the 

 usual dark or grey iris ; so, it is equally absurd to infer that 

 A. Grayana is not a Truncatella, because the white iris or pupil 

 was not detected. 



Dr. Gray concludes by stating, that my notions are not those 

 usually held by modern zoologists, and pronounces the whole of 

 my logic unsound. I am not surprised that my logic should 

 not find favour with one who considers that a genus must be 

 restricted in the number of its species, however similar these 

 may be in every essential character ; and am sorry to learn, on 

 Dr. Gray's authority, that such notions are held by modern 

 zoologists, of which I was not before aware. 



I am. Gentlemen, 



Your most obedient Servant, 

 William Clark. 



XXVI. — On the Morphology of the Organs called Lenticels. 

 By M. E. Germain de Saint-Pierre*. 



The name of lenticular glands was given by Guettard, and that 

 of lenticels by P. DeCandolle, to certain organs belonging to the 

 bark of a great number of plants, which appear at the surface of 

 the epidermis in the form of little brownish elevations or rugo- 

 sities of an oval or elliptical form. 



* From the Comptcs Rendus, August 20, 1855, p. 305. 



