1852.] 



57 



^ 



certainly seemed to accord very closely in size and shapt? with the upper jaw. 

 Any one who has observed the very close correspondence between the dentition 

 of suiline pachyderms, and the great variation in different portions of the dental 

 series, w-ll appreciate the difficulty of apportioning properly small fraiiments of 

 closely allied species, and will excuse the faults which I have unconsciously 

 committed. As the best reparation for these errors, I subjoin the following 

 synonyms of the fiagmcnts of the head, described by me : 



Hyops depressifrons Lee. Am. Journal of Sc 2d series, 5, 103. 



Dicot]jhs .depressifrons Lee. Proc. Ac. Nat. Sci. 6, 3. 



(In part.) Flatygonus comjnesstis Lee. Am. Journal, 1. c. and Trans. Am. 

 Ac. Arts, N. ser. 3, p. 1, 2, 3. 



Protocliariia frismaticin Lee. Am. Journal, 1. c. -5, 103: Proc. Ac. 6, 5. 



The fragments to be here referred, are a cranium: fragments of anterior part 

 of head with premolars and canines : the entire dental series of upper jaw : except 

 the last molar, the canine and two inferior molars of lower jaw, the latter be- 

 longing to a smaller specimen of perhaps another species. 



Platygonus c o m p r e s s u s Lee. Am. Journ. 1. c. and Trans. Am. Ac. 

 Arts. 



Lower jaw with twoposlerior molars : pi. 3, fig. 7. 



Upper teeth,* posterior molar and two premiolars : pi. 3, fig. 12 and 13, (left 

 hand.) 



Mt. Lea stated some of his views .regarding species, and mentioned that the 

 subject had engaged the attention of eminent naturalists, some of whom had given 

 definitions, which did not fulfil his idea of what constituted that term. Lindley, 

 in his Introduction to Botany, has given some very judicious and philosophic 

 views on classification. " Species," he says, " are created by Nature hersell, 

 and remain always the same in whatever manner they may be combined ; they 

 form the basis of all classification, and are the only part of it which can be con- 

 sidered absolute." In this he makes no attempt to define his ideas of species. It 

 is assumed to be a distinct creation, and unchangeable. 



MM. Ray and Drouet (" Revue et Mag. de Zoologie, 1849 "') give their views 

 of what forms a species, in the following terms : " Generalement on entend, par 

 ce mot, (espece) un type d'organization de forme et d'activite, rigoureusement 

 determine, qui se perpetue successivement par generation directe et d'une ma- 

 niere indefinie avec la meme Constance de caracteres." 



Milne Edwards' definition of species, Mr. Lea thought was less clear. He says, 

 " On donne le nom d'espece a la reunion des individus, que se reproduisent entre 

 eux avec les memes proprietes essentielles." 



Cuvier considered that the fact of the succession, and of the constant succes- 

 sion, constituted alone the validity of the species. 



Dr. Morton comprised his view of species, as "a primordial organic form." 



Neither of these definitions fulfil Mr. Lea's idea of what forms a species. It 

 seemed tohim,that a species must be considered to hez. primcay estaUished lati\ 

 stamped with a persistent form pertaining solely to itself, with the power of 

 successively reproducing the same form, and none other. 



Mr. Lea also stated he was about to issue a new edition of his Synopsis of thg 

 Family Naiades, with much additional matter. That in the introductory part, 

 he had given the classification of various zoologists, and among others those who 

 had divided the Naiades by their anatomical differences, viz: D'Orbigny, Tro- 

 schel, and Agassiz. In these he said it would be observed, by consulting the 

 works of the two first, and a work entitled " Shells of New England," by Mr. 



*The figures of these leeth were sn ban' I y drawn by the artist engaged by nie, and 

 still farther deteriorated and altered while in the hands of Mr. Endicoir, that the minute 

 differences which distinguish such cloFr'y allird nrvrrials are not lo be seen : in excuse 

 for permitting such figures to go before llie uur.d, I must say that the memoir was 

 printed during my absence on a scieatifie expedition, and that no opp(<rtunity was offered 

 for correcting the proof. 



