Oolitic Formations in the vicinity of Minchinhampton. 253 



Another generic form, as yet found in no other part of England, 

 is a conical turbinated univalve, called by me Trochotoma ; five 

 species occur, but only one is common. Its distinguishing generic 

 feature is a transverse fissure upon the body-whorl, which ap- 

 proaches the outer lip, but does not reach it. This alone is suffi- 

 cient to distinguish it from Pleurotomaria, from which also the 

 base materially differs, its deep concavity resembling an umbi- 

 licus and giving to the aperture a semilunar figure. 



The outer lip is thick, the whorls usually angular and concen- 

 trically striated. They occur throughout all the lower fossiliferous 

 beds. Perhaps I may be excused for briefly alluding to the 

 name given to this shell, although the matter is of a somewhat 

 personal nature. In the autumn of 1841, finding that this form 

 was entirely unknown, I forwarded a specimen to Prof. Sedgwick 

 as a new genus, and mentioned that I proposed to call it Tro- 

 chotoma : about the same time a gentleman who then collected 

 largely from our Great Oolite and distributed its fossils widely 

 always affixed to it the name which I had proposed to give it, so 

 that the appellation became current wherever a collection of our 

 fossils existed six years ago. Within two years afterwards Pro- 

 fessor Ansted figured one of the species in his work on Geology 

 under the same name. Knowing these facts, my surprise may 

 be imagined, when lately turning to a new work on Natural 

 History by Pictet, published at Geneva, I found that he had 

 described this genus under a new name, saying that this is the 

 Trochotoma of M. Deslongchamp, and referring to a paper by 

 that gentleman on the Great Oolite of Normandy, published in 

 the 7th volume of the ' Transactions ' of the Linnsean Society of 

 Normandy in 1842. In that memoir are figured and described 

 five species, of which three are found in this vicinity. It would 

 therefore appear that M. Deslongchamp must have read his paper 

 to the Society in 1841, and nearly simultaneously with myself 

 must have imagined the same new word as a designation for a 

 certain new form. The paper in question is even now so little 

 known in this country that I was compelled to resort to the Bri- 

 tish Museum to see a copy of it. Probably another coincidence 

 exactly similar to this is not upon record. 



It is proposed to restore the forgotten term Cylindrites used 

 by Llwhyd as a generic name for a form which requires to be 

 distinguished, and which appears to be very characteristic both 

 of this rock and the Inferior Oolite. We possess six species, 

 three of which have been figured, two as Actceon in the l Mineral 

 Conchology/ and one as Conus by Archiac ; the generic charac- 

 ters are as follows : — Form cylindrical. Spire small, acute, some- 

 times not rising above the body -whorl but always exposed ; 

 whorls several, usually flat, sulcated at their junctions. Aperture 



