Dr. J. E, Gray on the Tongues of Mollusca. 415 



lor example, frequently described the parts of the mouth of a 

 single species as giving family characters, when, by the exami- 

 nation of several species, he would have been placed in a position 

 cither to form several families, or to have circumscribed the cha- 

 lacters of his famihes differently." I have only to observe, that 

 Dr. Troschel and I have gone on the same principles, because we 

 have worked from the same source, viz. Dr. Loven^s memoir; for 

 I have not been able to see a copy of Dr. TroscheFs work, and 

 ]iad overlooked the abstract in the ^Archiv,^ until my atten- 

 tion was called to the divisions in Dr. Troschel's paper above 

 quoted, and I was desirous of finding out when they were first 

 characterized. 



In the outline of the system I took care to consult my own ob- 

 servations, and to combine in it all the accounts of the teeth of 

 the different species of Gasteropodous Mollusca which had then 

 (1850) been published, and regret, as much as Dr. Troschel can, 

 that there were not more materials derived from different species of 

 the same genus and family to be used. I do not find the neces- 

 sity of making any alterations in that system from the genera 

 and species since described, except that of separating Ovula from 

 Cypraada, — unfortunately, however. Dr. Troschel's paper does 

 not afford me the means of characterizing the family Ovulidce — ; 

 and removing the genus Sycotypus from Muricida, and placing 

 it provisionally as the type of a new family differing from Lamel- 

 lariadce in the want of a trunk or proboscis. 



While on the subject I may further observe, that if there is 

 this difficulty of distinguishing the genera unless we have the 

 shell and the animal, with its operculum, tongue, and other 

 organs complete, we can well understand that there must exist a 

 similar difficulty in distinguishing species except under similar 

 circumstances. 



This is especially the case with the shells which, like the Pa- 

 tellcB, Emarginulce, Fissurellee, Calyptraa and Crepidula, have large 

 apertures, the animals of which rest for a long time in a parti- 

 cular station. 



In such instances, I am induced by experience to believe that 

 geographic situation is a character of much importance. The 

 very great variations which Patella vulgata and P. pellucida ex- 

 hibit on our coast. Patella saccharina on the coast of the Cape, 

 and Patella zebrina on the coast of South America, would scarcely 

 be believed, if we did not know that they all came from the same 

 localities, and did not sometimes find specimens which exhibit 

 two or more varieties or nominal species on the same individual, 

 the animal having changed its place twice or more during its life. 



I believe that it will be utterly impossible to make a proper 

 description of the species of these genera of Mollusca, until we 



