Letter from Professor Nicholson. 237 



111 the paper to which I Jiave alluded, you come to the conclusion 

 that the differences which separate the genera Conchicolites and Ortorda 

 are of merely specific value, and that the species which I have named 

 OHoma conica and 0. minor, will have to stand as Conchicolites conica 

 and C minor. As regards this point, you must allow me to remark 

 that your conclusion is illegitimate, and not, under any circumstances, 

 permissible. The validity, or the reverse, of a genus, is invariably 

 tested by the first species of the genus which may have been described, 

 and no genus can be abolished upon the ground that species not belong- 

 ing to it have subsequently to its definition been placed under it. It 

 is possible (though I do not think it to be the case), that there may 

 be nothing more than specific diflerences between the forms described 

 by me as Conchicolites corrugatus, Ortonia conica, and 0. minor; but 

 this could in no way affect the value of the genus Ortonia. My genus 

 Conchicolites was not founded upon C. cornigatns, but upon C. gregarius; 

 and tbe characters of this latter are beyond all question such as to 

 demand a generic separation from the forms subsequently referred by 

 me to Ortonia. 



If, therefore, you should prove to be right as to the close affinity 

 between Ortonia conica and Conchicolites corrugatus, you would still be 

 in error as to the conclusions which you draw from this fact. Instead 

 of this fact necessitating the abolition of the genus Ortonia, and the 

 reference of 0. conica and 0. minor to the genus Conchicolites, it would 

 simply necessitate our removing Conchicolites corrugatus to the genus 

 Ortonia. We should thus have under Ortonia the three species, 0. 

 corrugatus, 0. conica, and 0. minor ; and the genus Conchicolites would 

 then contain only the single species, C. gregarius. I do not think that 

 this course will be adopted; for the specimen described by me as Con- 

 chicolites corrugatus was very unlike those which I refer to Ortonia, 

 more especially in the fact that the tubes are only attached by their 

 bases ; but under any circumstances, the validity of the genus Ortonia 

 will remain unaflTected. 



In the second place, it is implied that I did not give credit to Dr. H, 

 H. Hill for the discovery of the specimen of Conchicolites corrwjutm 

 described by me. As regards this point, I would simply mention that 

 (as stated in my paper,) the specimen in question was forwarded to 

 me by Prof. Orton, that the name of its discoverer was not mentioned 

 to me, and that I Avas consequently unable to state l)y whom it had 

 been discovered in the first place. Indeed, from the fact that Prof. 

 Orton, no doubt from pure inadvertance, did not mention to me who 

 had discovered the specimen, I presumed that it belonged to the State 

 collection. Whilst, therefore, my apologies are due to Dr. Hill for 



