July 25, 1878] 



NATURE 



327 



new genera are described, with twelve new species out of 

 a total of thirteen. In addition to these new species 

 there were but seven others which, so far as their identi- 

 fication was possible, were already known as European 

 forms. The collection had been preserved in spirits and 

 was for the most part in excellent preservation. It would 

 seem obvious that the region from which this collection 

 had been obtained, and which includes an area between 

 the Florida Reef on the north and west and Cuba the 

 Salt Key and Bahama Banks on the south and east, is 

 characterised by a very distinct hydroid fauna, and must 

 form part of a special province in the geographical distri- 

 bution of the Hydroida, though of course further re- 

 searches may greatly extend the area of the new forms. 

 The greatest depths at which any species had been 

 dredged was 470 fathoms. The collection was rich in 

 the plume-like hydroids (Plumulariadae). In some genera 

 of this beautiful family of hydroids the ultimate gene- 

 rative zooids which give origin to either the germ 

 or the sperm cells (gonophores) are developed within 

 a horny covering (gonangium), groups of which are 

 often to be found inclosed in most curious basket-like 

 receptacles (corbula). Such basket-like receptacles are 

 well seen in Aglaophenia, and in a new species described 

 as A. bispinosa, they attain a very large size and form 

 most beautiful objects. In this genus the twigs of the 

 cradle are much altered pinnae which are pressed into a 

 protective service. In one of Dr. Allman's new genera 

 nearly allied to Aglaophenia (Cladocarpus) the groups of 

 gonangia are not inclosed in corbulae, but are borne on 

 the sides or at the base of special protective branches 

 which are not altered pinnae but appendages to them. 

 They certainly seem to act the part of corbulas, and to 

 form very effective organs of defence to the gonangia — 

 though they do not present so effectual a covering as in 

 Aglaophenia. In one magnificent species {Cladocarpus 

 paradised) the stem of which attains a height of 

 fourteen inches, these phylactogonia, as Dr. AUman 

 calls them, are in the form of pinnately-branched 

 offshoots. In another species {Cladocarpus doli- 

 chothecd) the stem for nearly the whole of its course 

 carries a longitudinal series of tubular receptacles which 

 contain sarcode in which thread-cells are found. These 

 nematophores, which are situated at short and equal 

 intervals from one another, give to this part of the 

 hydroid colony a very close resemblance to certain forms 

 of graptolites. Elsewhere Dr. Allman has called atten- 

 tion to the close affinity that appears to exist between the 

 so-called denticles of the graptolites and the nematophores 

 in these Plumularian hydroids ; and, as we know, that 

 these bodies in the hydroids are not only filled with pro- 

 toplasm, and that this is capable of developing pseudo- 

 podia after the manner of some rhizopods, this might 

 seem to point to a relationship between the graptolites and 

 the rhizopods through some ancestral form in which the 

 affinities looked on the one side to the hydroids and on 

 the other to the rhizopods, the graptolites having stopped 

 short of the progress which the hydroids were enabled to 

 make. 



The beautiful plates illustrating this memoir have been 

 executed by the faithful pencil of Mr. Hollick, though the 

 details of structure have been drawn by the skilled and 

 practised hand of the author. E. P. W. 



OUR BOOK SHELF 



Automatic Arithmetic : a New System for Multiplication 

 and Division without Mental Labour and withotit 

 the Use of Logarithms. By John Sawyer, Public 

 Accountant. (London : George Bell and Sons, 1878.) 



This is an ingenious work, and would have suited the 

 " fantastical " Armado (" I am ill at reckoning ; it fitteth 

 the spirit of a tapster"). By the aid of 1759 figures 

 only the user of it is able to multiply any two numbers 

 each not exceeding 999,999,999, and also to divide one 

 number by another, neither exceeding the same limits. 



Its advantage over logarithms, in the cases to which it 

 applies, is that the results are accurate instead of approxi- 

 mate. 



The principle of construction is very simple : take ten 

 pages ; at the top of each write the nine digits in succes- 

 sion (for facility in working, the numbers are printed red 

 and black alternately) ; cut each page into nine horizontal 

 sections, and at the end of each strip write the same 

 number (viz., for the fifth page the constant number witl 

 be 4), then on each strip will be printed 



04 08 12 16 20 . . . 36 



the printing being so arranged that each strip shall have 

 the numbers of the previous strip printed one place further 

 to the right. From this description it will, we think, be 

 readily seen how to apply the tables to multiplication. 

 To take a very simple example (any other example coming 

 within the limits we have specified can be worked with 

 almost equal facility), multiply 374 by 7. 



Take the larger of the two numbers ; turn back all 

 the top row slips above 3, then all the second row 

 slips above 7, then all the third row slips above 

 4, then carry the eye down the vertical column corre- 

 sponding to the number, and we see (in this case in 

 black figures) — 



21 



49 

 28 



whence, adding, the result is seen to be 2618. 



Each additional figure in the multiplier gives a result 

 similarly obtained, and the answer is got by no mental 

 operation more difficult than simple addition. A mere 

 child who can add numbers together can thus perform 

 mechanically (or automatically) difficult exercises in mul- 

 tiplication. Division is similarly reduced to subtraction. 

 Whether much saving of time and labour is effected is a 

 question we leave to practical men. We showed the 

 work to a class of boys, and they were much interested 

 in watching the process, the principle of which was 

 readily understood by them. 



Numbers can thus be easily raised to powers, but 

 the method does not serve for the extraction of roots. 

 We need hardly state that the tables are protected by 

 letters patent. 



A Handbook of the Plants oj Tasmania. By the Rev. 

 W. W. Spicer, M A., &c. (Kobart Town : J. Walch 

 and Sons, 1878.) 



This little book of 160 pages contains a great deal more 

 valuable matter than would at first sight appear. The 

 author justifies the production of his book from the fact 

 that previously existing works treating of Tasmanian 

 plants are though " works of extraordinary merit, costly 

 and ponderous,' ' in proof of which he points to the labours 

 of Hooker, Mueller, and Bentham, all of whose works are 

 undeniably of very great value, but if for no other reason 

 than their bulk, quite unfitted to be the companion of a 

 botanical ramble. The book before us is intended for 

 this purpose, being convenient in size, and as the author 

 tells us in his preface, "moderate in cost." With regard 

 to the plan of the book, the author's own description will 

 make it more clear than any words of our own. He says. 



