522 Revieus — WacJismuth ^ Springer's Monograph on Crinoids. 



an adequate idea of the scope of the completed work." At the 

 outset we are surprised that a sura of five shillings should be 

 charged for so comparatively meagre a volume. We judge that 

 the whole of it is reprinted from the Quarry newspaper, in 

 whose jiages " the latter portion is still appeai'ing " ; and the 

 information now given relates chiefly to geological surveying, to 

 dips, outcrops and faults, to unconformities and overlaps, and other 

 matters. Tliese are well illustrated with diagrams, many of theiti 

 being after the style of Sopwith's famous models. A good deal 

 of space is occupied with mathematical calculations having reference 

 to the determination of the true dip, and to the throw of faults and 

 dislocated veins : information of questionable value to the practical 

 man. A final chapter of twenty pages deals generally with the 

 economic minerals which occur as stratified ore-deposits. As already 

 stated it is not possible to judge fully of Mr. Elsden's work. So 

 long ago as 1816 William Smith lamented that " the theory is in 

 possession of one class of men, and the practice in another." 

 This state of things is not wholly unknown at the present time, 

 and if Mr. Elsden succeeds in his task of welding the two together, 

 his labour will not have been in vain. 



T 



V. — Wachsmuth and Springer's Monograph on Crinoids.^ 



Fourth Notice. 



HE Abactinal system of the Crinoid skeleton comprises the 

 elements of the Stem and appendages, the Patina (in which 

 are included only IBB, BB, and ER), and the dorsal ossicles of 

 the Arms. Our authors' account of the two former has already 

 been passed in review. Their description of the brachials (pp. 73-88) 

 needs no elaborate discussion, since the controverted points were 

 dealt with in an earlier notice. Let it be noted, however, that 

 all abactinal elements beyond the five radials belong to the arms. 

 Therefore, every normal crinoid has five arras. Each arm may 

 remain single, or may fork once, or may fork an indefinite number 

 of times, either regularly or irregularly. The branches into which 

 it forks may be of equal or of very unequal size. The proximal 

 regions of the arms may be incorporated with the patina to form 

 the dorsal cup. The portion so incorporated is said to be ' fixed ' ; 

 the remaining distal portion is termed ' free.' If only the priraibrachs 

 of an arm be fixed, then the secundibrachs will be free, and it will 

 appear as though two arms left the calyx in that ray. If the 

 secundibrachs be fixed, and the tertibrachs free and equally 

 developed, then there will appear four free arms in the ray. 

 But to say that the former crinoid has actually two arms to the 

 ray, i.e. ten arms altogether ; or that the latter has twenty 

 arms — such statements breed confusion. Yet they are constantly 

 made, and they are to be found in the present Monograph. 

 A crinoid may have almost any number of arms [Tetracrinus has 



1 The North American Crinoidea Camerata. By C. "Wachsmuth and F. Springer. 

 Mem. Mus. Comp. Zool. Harvard, vols, xx and xxi, containing 838 pp. and 83 plates. 

 (Cambridge, U.S.A., May, 1897.) For First, Second, and Third Notices, see 

 June, July, and September Numbers. 



