Quarterly Journal of Conchology. 93 



CONCHOLOGICAL DIFFICULTIES; or, SPECIES 

 VERSUS VARIETIES. 



By EDWARD SIMPSON. 



In looking over a collection of shells, or in reading the 

 description of them by various authors, the student is apt to get 

 greatly confused, and to wonder why there are so many species, 

 and what can be the principle upon which they are formed. In 

 order to explain what I mean, I propose going through the works 

 of several authors, and comparing them together, I will first give 

 an extract from Jeffrey's British Conchology, vol. i., page xvii. of 

 the introduction, where he says " Certain definite forms, called 

 species, exist ; and that they constitute, more or less extensive 

 groups of individuals, which resemble each other, as well as their 

 parents and offspring, to the same extent as we observe in the case 

 of our own kind. These groups, to deserve the name of species, 

 must be distinct from others ; because, if any of them are so inti- 

 mately blended together by intermediate links, so as to make the 

 line of separation too critical, the test fails, and a subordinate 

 group, or what is called a 'variety,' is the result. For this reason it 

 is indispensably necessary to compare as great a number of indi- 

 viduals as possible ; and especially a series of different ages and 

 sizes, commencing ab ovo, as well as specimens collected from 

 various localities." Hethen goes on to speak of the right of every 

 naturalist : " To follow the bent of his own discretion or inclina- 

 tion in the extension or reduction of species, subject only to the 

 opinion of his scientific compeers," and then speaks of varieties : 

 " Besides species, and holding a subordinate rank to them in the 

 great host of Nature's works, are certain forms, called ' varieties,' 

 which are not less definite, but more difficult to separate from 

 their typical or specific form. They are off-shoots of species, and 

 originate in some peculiarity of climate, situation, composition of 

 soil, or water which they inhabit ; the nature or supply of food, 

 and various other conditions. The characters by which they 

 usually differ from species consist of size, comparative proportions 

 of different parts, colour, and degree of sculpture, and the investi- 

 gation of forms thus changed, or modified is often extremely per- 

 plexing." * * * * * " Varieties are of two kind.s 

 — permanent and local. The former are called * races,' and have 

 many of the characters of true or typical species with which they 

 associate." And further on he adds : " I believe it may now be 

 considered a well-established rule that all distinct groups of indi- 

 viduals living together, and having common feeding ground, and 

 which are not connected or blended with each other by insensible 

 gradation, ^xg. prima facie entitled to the rank of species. A con- 

 trary opinion used formerly to be entertained by some naturalists, 

 and it was not unusual to found a claim to specific distinction on 

 the fact that the specimen thus distinguished, did not occur with 



