Dec. 27, 1888] 



NATURE 



Q7 



a dermal bone of the cranial roof of a Dipnoan, an 

 interesting bone of Ctenodus being figured for comparison. 

 The Old Red Sandstone fossil, named Phyllolepis con- 

 centrictis by Agassiz, is also interpreted as probably the 

 head-bone of a closely-allied fish ; and the remarkable 

 skull-fragment known as Archceonectes pertusus, H. von 

 Meyer, is considered to be the bony portion of the palate, 

 wanting the teeth. 



To the appended synopsis of the literature of the sub- 

 ject, we might add two important papers on Ctenodus, by 

 W. J. Barkas, published in the Proceedings of the Royal 

 Society of New South Wales, 1876-77 ; and the list of 

 known Palasozoic Dipnoan fishes must be reduced by one 

 (S/rigiltnd), which is founded upon a tooth of a Selachian. 

 We would also remark that the so-called Campylopleuron 

 is almost certainly founded upon the tail of Ctenodus, as 

 pointed out by Dr. Traquair (Nature, vol. xviii. p. 483). 

 In every respect, however, the memoir affords evidence of 

 the most elaborate and painstaking research ; and it must 

 long remain a standard work of reference for all who are 

 interested in the palaeontology of the Dipnoan fishes. 



A. S. W. 



OUR BOOK SHELF. 



A Revision of the Heterocyst Nostocacece. By Ed. Bomet 



and Ch. Flahault. (Separate reprint with index.) 



(Paris, 1886-88.) 

 In this very important contribution to our knowledge of 

 this interesting group of Algae, the publication of which 

 commenced in the third volume of the Annates des 

 Sciences A'aturettes, vu. scrie (1886), and was concluded 

 in the seventh volume, published this year (1888), we have 

 a work of great labour and research, upon the happy 

 completion of which the authors are to be congratulated. 



Those who have investigated the forms of these Algae 

 will remember the extreme difficulties they have ex- 

 perienced in determining the so-called species of many of 

 the authors whose works they were obliged to consult. 

 Too often it has happened that, unable to recognize a 

 form collected, it has been described as new, and so but 

 added to .the big pile of synonyms. 



Accepting the division of the hormogonous Nostocs into 

 the two subdivisions of those with "uniform cells" and 

 those with " dissimilar cells," it is with the latter group 

 that the present " Revision " has to do. For many years 

 the authors have investigated all the examples, living or 

 dried, that they could procure. The herbaria of Brdbisson, 

 Chauvin, Grunow, Lenormand, Thuret, and the collec- 

 tions of the Museum of Paris, have all been consulted, 

 with the result that an immense mass of described species 

 have been treated as synonyms ; while a certain number, 

 of which type-specimens were not to be had, or on 

 account of difficulties of referring them to known genera, 

 have been enumerated as " species inquirendae." 



Introductory to the description of the genera and 

 species we have an account, up to the present state of our 

 knowledge, of the vegetative cells, the filaments, and the 

 trichomes, the outer envelope (cytioderm),the heterocysts, 

 the ramification, the hormogonia, and the spores. Of 

 these two latter modes of reproduction, that by the 

 "hormogones" has been the longest known, and is the 

 one to be found in most of the genera ; while that by 

 " spores," destined to preserve the species during the 

 intervals of vegetation, and enabling it to resist desicca- 

 tion, is known only to occur in some few of the genera, 

 but the authors add " that it is permissible to think that 

 it will soon be known to occur in all." These spores are 

 easily distinguished by their size, their more rounded 



form, and their more marked granular contents. They 

 often possess a brownish-yellow epispore ; in some in- 

 stances they have been proved to retain their vitality 

 for a considerable time ; the spores of Cylindrospcrutn 

 licheniforme, Kutzing, have germinated after a nine years' 

 sojourn in a dried state, in an herbarium. About their 

 behaviour just at the period of germination we have still 

 something to learn. The "conidia" of Borzi are also 

 alluded to. A conspectus of the genera of each of the four 

 tribes of the sub-family is given ; the four tribes recog- 

 nized being the Rivulariaceae, Sirosiphoniaceae, Scytone- 

 maceae, and Nostocaceaj. After the list of genera comes 

 the list of species, with analytical keys and detailed 

 diagnosis of each. There is a very full account of the 

 geographical distribution of all the species. 



In a notice the main object of which is to call the 

 attention of our readers interested in these for the most 

 part fresh-water Alg^, it would not be proper to enter into 

 minute details, so we will content ourselves with a state- 

 ment of our belief that this memoir of Dr. E. Bornet and 

 M. Flahault will not only do very much to assist the 

 botanist, but will also go far to awaken a new interest in 

 a group of plants in which there is abundant field for 

 further research. E. P. W. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 take to return, or to correspond with the writers of, 

 rejected manuscripts intended for this or any other part 

 of Nature. No notice is taken of anonymous communi- 

 cations. ^ 



Mr. Spottiswoode's Mathematical Papers. 



At the request of Mrs. Spottiswoode, I have undertaken to 

 edit these papers. Mrs. Spottiswoode has kindly looked over 

 her collection, and put into my hands author's copies of such 

 papers as she has. I still lack the following, which some one or 

 more of the late President's friends may perhaps be able to lend 

 me. The numbers are those of the Royal Society's Catalogue. 



I. Phil. Mag., xxxvi. (1850) ; VI. Crelle, xlii. pp. 169-78 ; 

 VIII. Tortolini, Annali, iii. (1852) ; IX., X. Camb. and Dub. 

 M. fourn., viii. (1853); XIII. R.S. Proc, vii. (1854); XX., 

 XXI. same, xi. (i860) ; XXII. [as regards Geog. Soc. Proc, 

 v. (1861)] ; XXIV. Brit. Assoc. Report (1861) ; XXV. Crelle, 

 lix. (1861) ; XXXIII. [as regards Quart, fourn., vi. 1864]; 

 XXXVII., XXXVIII., Quart. Journ., vii. (1866); XLVIII., 

 XLIX., and some other papers in the Comptes rendus (1874-76). 

 I am especially anxious to receive \!nQ. first part of the " Medita- 

 tiones Analyticte," of which we have not found a complete set. 

 All the papers are in Mrs. Spottiswoode's library, she believes ; 

 but I am anxious to preser/e the^e if possible from passing into 

 the printers' hands. R. Tucker. 



27 Cantlowes Road, N.W, 



Statistics of the British Association. 



It is to be feared that the " ladies' curve " in the diagram 

 (Nature, December 13, p. 153) fails to give anything like 

 accurate information respecting the number of ladies at the 

 meetings of the British Association. Omitting foreigners, the 

 attendance is made up of "members," "associates," and 

 "ladies," but, as a matter of fact, a large number of ladies 

 are members or associates, while only the remainder take 

 "ladies' tickets," — that is, tickets transferable to ladies, the only 

 transferable tickets issued by the Association. 



The column headed " Ladies," in the table (see the Associa- 

 tion's Report for 1887, pp. Iv.-lvi.) states that 493 ladies 

 attended the last Manchester meeting ; but that merely shows 

 that 493 of the ladies who were present took "ladies' tickets," 

 and does not include the lady members and lady associates who 

 were at that meeting. During its meetings the Association pub- 

 lishes lists of the members and associates who are present, 

 exclusive of the holders of "ladies' tickets." By going over the 

 Manchester lists it will be found that upwards of 700 ladies who 

 were either members or associates were in attendance ; so that. 



