SYNOPSIS OF 



Of the subgenus Iridina (Lamarck), there are 3 species, and 1 unknown to me. 1 

 Of the subgenus Spatha (Lea), there are 4 species, all recent. 

 Of the subgenus Mycetopus (U Orbigny) , there are 3 species. 



Most of the distinguished authors who have written on the subject of the division of 

 this Family, have acknowledged the extreme difficulty they have encountered in separat- 

 ing it into subdivisions. This difficulty is not peculiar to the Naiades. In most of the 

 families where a great number of species have been observed, we find these species so 

 merging, and, in some of their characters, so fading away into each other, that we scarcely 

 know how — indeed, in some instances it is impossible — to make the separation with pre- 

 cision. "Natura non facit saltum." In the vegetable kingdom, the same obstructions to 

 a system are encountered. The observations of Lindley 2 are so just and philosophic, that 

 I cannot refrain from quoting them here : — 



"Species are created by Nature herself, 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 considered absolute. For although, in a natural system, all other 

 combinations — whether genera, tribes, orders, or by whatever name they may be known — 

 comprehend species agreeing much more with each other than with anything else, and 

 having a positive general resemblance in the majority of their features, yet no fixed limits 

 can be assigned to any of them; on the contrary, they pass, by means of various inter- 

 mediate species, into the other genera, tribes, orders, &c, to which they are most nearly 

 allied. For this reason, viz., that no fixed limits can be assigned to orders, genera, &c, 

 we find the ideas about them fluctuating with the degree of our knowledge; which is the 

 true cause of those changes in the limits of genera, &c, which persons unacquainted with 

 the subject are apt to consider arbitrary, but which, in skilful hands, are dependent upon 

 a progressive advance in the knowledge of science." 



MM. Ray and Drouet (Revue el Mag. de Zoologie, 1849) give their views of what forms 

 a species in the following terms: "Generalement on entend, par se mot (espece), un type 

 d'organization de forme et d'activite, rigoureusement determine^ qui se perpetue successive- 

 ment par generation directe et d'une maniere indefinie avec la meme Constance de caracteres." 



Milne Edwards's definition of species, I think, is less clear. He says : " On donne le 

 nom d'espece a la reunion des individus, que se reproduisent entre eux avec les memes pro- 

 prietes essentielles." 



1 Mr. Gray, in his Genera, gives priority to Scopoli, 1777, under the name of Mutela. I have not access to 

 Seapoli's works, and, therefore, for the present, retain Lamarck's well-known name of Iridina. 

 3 See Introd. to Botany, p. 307. 



