Reviews— Wach smut h (f Springer's Ilonograph on Crinoids. 423 



suggestion of Dr, J. Walther's. It is here alluded to with the view 

 of emphasizing the fundamental distinction between Monocyclic and 

 Dicjclic crinoids. 



Another hypothesis — the descent of Monocyclica from Dicyclica — 

 stands on a different footing. No one has done more than 

 Wachsmuth and Springer to point out that the infrabasals often 

 diminish in size, become hidden beneath the stem, and may 

 eventually disappear altogether, at least in the adult. At the same 

 time they have insisted on important differences between such forms 

 and those that were without infrabasals from the beginning. To 

 express this conception in nomenclature I proposed the term Pseudo- 

 monocyclica for crinoids with obsolete infrabasals. The differences 

 just alluded to are identical with certain differences that always 

 (or almost always) obtain between Dicyclica and Monocyclica, and 

 have been summarized in the well-known Law of Wachsmuth and 

 Springer. They are diagrammatically represented in Fig. 2 : — 



Fig. 2. — Comparison of the dicyclic and monocyclic base. B, basal ; Br, brachials 



marking the five rays ; ci, cirri, only three out of the five are shown ; 



CO, pentameres of column ; IB, infrabasal ; n, nerves going to cirri ; 

 E, radial ; s, sutures between pentameres of stem. 



The law is given in the Monograph under review in the form of 

 a table (p. 60), and may be stated thus: when infrabasals are, or 

 have been, present, the exterior angles and the pentameres of the 

 stem are interradial (ie. alternating with IBB), but the longitudinal 

 sutures, the sides, the lobes of the axial canal, and the cirri of the 

 stem are radial ; in crinoids with a truly monocyclic base these 

 positions are reversed. "This law," its authors observe, "is only 

 applicable, to its full extent, in species with pentangular or 

 pentapartite stem and canal." Unfortunately it is not universally 

 applicable even to those, and although the law as it stands is 

 a remarkable piece of induction from which have been deduced 

 conclusions at first unexpected but subsequently proved, yet it 

 requires placing on a firmer basis before it can be accepted as other 

 than a purely empirical statement liable to random exceptions. 



This basis I shall now attempt to furnish. But first let us 

 consider the exceptions. Wachsmuth and Springer say there are 

 two, " and, so far as we know, only two. In Pentacrimis [^=zIso- 

 crinus'] and the monocj'clic Ghjptocrinus FornsheUi, S. A. Miller, 

 the axial canal has the same orientation as the outer angle of 

 the stem." Other examples could be adduced from the Silurian 

 crinoids of England and Gotland, but those given serve to show 



