March 1, 1870.] HARDWICKE'S SCIENCE-GOS SIP. 



55 



GUANO DIATOMS. 



A FTER all that lias been written of late against 

 -^- the very extensive, and too exclusive, study 

 of the Diatomacea? prevalent amongst microsco- 

 pists, and considering the prejudice which to 

 some extent evidently exists against the study, on 

 account of the supposed undue share of attention 

 which it has received, it is not without some hesita- 

 tion that I venture to contribute a paper on 

 diatoms. And this hesitation is not lessened by 

 the fact that I have to make some remarks on the 

 so-called "fossil diatoms" and some of their un- 

 usual forms, of which, when no living examples of 

 similar kinds have been found, doubts are enter- 

 tained whether they should occupy any position 

 whatever in the scientific classification of the 

 Diatomaceae. 



Eor some time past, during the leisure time at 

 my disposal, I have made extended examinations of 

 guano, and I have prepared many slides, by the 

 method of selection, of which there is a description 

 in SciENCE-Gossir, vol. i., and a further account in 

 the second number of the Monthly Microscopical 

 Journal. Perhaps an account of some of the results 

 of my search may contribute to Microscopical Re- 

 creation, if not to " Microscopical Research." 



In common Peruvian guano, besides the forms 

 usually met with, I have found two specimens of 

 Aulacodiscus Kittoni, a form, according to Prit- 

 chard, usual in New Zealand and Monterey Bay, 

 and fossil in Monterey stone. I notice that in my 

 specimens the row of marginal dots given in the 

 figure by Pritchard is entirely wanting (fig. 52). 



Fig. 52. Aulacodiscus Kittoni, x 350. 



I have also met with two very interesting and 

 perfect specimens of an Auliscus, which I suppose 

 to be new. The accompanying figure will give a 

 clear idea of the form and markings of this diatom. 

 The species to which it bears the closest resem- 



blance is, I think, Auliscus racemosus {Microscopical 

 Journal, vol. iv., new series) ; yet the difference of 

 structure is greater than that usually required to 

 mark a distinct species (fig. 53). 



Fig. 53. Auliscus, x 350. 



Another form, which I take to be one of the 

 valves of a large Biddulpliia, is also worthy of notice 

 (fig- 54). 



Fig. 54. Biddulphia, sp., x 350. 



There is yet another example of singular forms 

 to which I would direct attention. It is a diatom, 



