230 



THE AMERICAN MONTHLY 



[Aug., 



Five or more spines. No equatorial girdle. 



D. — RADIAL CHAMBERED ARMS. 



Three arms, regular. 



Three arms, bilateral. 



Four arms, membrane. 



Four arms, no membrane. 



Four arms, terminal membranous girdle. 



Five arms. 



16.— Family: SPONGODISCIDA. Spongy. 

 Three radial spines. 

 Five to ten or more. 

 None. 



{To he continued.) 



Stylodictya. 



Hymeniastrum . 



Euchitonia. 



Histiasirum. 



Stauralastrum. 



Ste-phanastrwm. 



Pentinastrum. 



No sieve plates. 



Spongotripiis. 



Stylotrochus. 



Spongodiscus. 



Review of "Modern Microscopy : a Hand-book for Begin- 

 ners by Cross and Cole." 



By Dr. W. H. Dallinger, 



LONDON, ENGLAND. 

 [ From Nature, July 13, 1893. ] 



This book although only extending to 104 pages, is what it 

 professes to be, and will prove thoroughly useful to beginners. 

 The authors understand practically their respective subjects, and 

 this has given the capacity, never otherwise possessed, to tell 

 the beginner accurately and efficiently what it is needful for 

 him at the outset to know. 



It is highly to be commended that they have not rendered 

 their pages incompetent by any pretense at an introduction to 

 the optics of the instrument or concerned themselves with any 

 attempt at exposition of modern optical theor3^ They have 

 done what affords a more genuine evidence of their appreciation 

 of the importance of these subjects, having presented the results 

 of the study of them in a practical form to the beginner so that 

 although his earlier efforts are not complicated with mathemat • 

 ical demonstrations and theory, he is nevertheless taught to 

 work, on the highest results reached through these, so far at 

 least as they apply to his initial endeavours. 



The danger of extremely elementary books on microscopy is 

 shallowness. They have often been a mere catalogue of two or 



