(2) 



TYPICAL OBJECTS IN NATURAL HISTORY. 109 



what objects they regard as most typical of those groups and their principal 

 subdivisions. May I request that returns be made as speedily as con- 

 venient, and that they be not delayed beyond the end of this month, or at 

 furthest the middle of the next ? 



As an example of what may be considered sufficient for the purpose in- 

 tended, I here subjoin the information afforded me by Mr. Darwin, whose 

 close study of the Cirripedia has rendered him so competent a judge of what 

 may be regarded as the most typical species of this group of animals. 



J. S. Henslow. 



[N.B. — The list referred to is inserted under Crustacea.'\ 



P.S. I would further suggest, that where the best type is not a British object, 

 some British species in addition (the more common the better), belonging 

 to the same group, should be named. These, being superadded to the typical 

 series, will point out the full extent to which the groups illustrated occur in 

 Britain. 



In regard to tj'pical objects for a geological series, I would suggest some 

 Buch formula as the following to be filled up and forwarded : — 



Under each formation, its — 



I. Lithology. 

 Typical rock specimens {ex. gr, from Red Crag) : — 



Comminuted shells, more or less cemented by oxide of iron. 

 Detrital materials from the lower beds, viz. rolled and altered 

 fragments of Septaria, phosphate nodules, and a few characteristic 

 fossils from London Clay, from Coralline Crag, &c. 



2. Simple minerals frequently associated with the rock, series (ex.gr, from 

 London Clay) : — 



Gypsum (crystals), Iron Pyrites (nodules). 



3. Illustrations of volcanic agency : — 



(1) Rocks ejected during the period. 



(2) Rocks modified by eruptions subsequent to the period in question 

 (ex. gr. coal charred, limestone crystallized, by incursion of trap in 

 dykes subsequent to the consolidation of the coal-measures). 



II. (Botany) Flora. 

 Best examples for proving the fact, that either or each of the three Natural 

 Classes have been met with in the formation illustrated : — 

 (3) Acotyledones. 

 (2) Monocotyledones. 

 (1) Dicotyledones. 



III. (Zoology) Fauna. 

 One species of one or more genera characteristic of the formation in each 

 Class, and its main subdivisions, as. 



Classes or Subclasses. Example of Subdivisions. ' 



Amorphozoa. 

 Foraminifera. 

 Zoophyta. T Crinoidea. 



Echinodermata < Asteroidea. 



— l^ Echinoidea. 



Annelida. 



Crustacea Cirripedia. 



Insecia. 



