Reviews — Wachsmuth (f- Springer^s Monograph on Crinoids. 525 



all lie above the level of the deltoids, which may thus be almost 

 entirely obscured. Where the covering-plates, especially the five 

 proximals, ai-e well developed and preserved the deltoids are 

 scarcely to be detected ; but where they are small the deltoids 

 are often conspicuous. Hence these two distinct sets of plates 

 have occasionally been confused. That they are absolutely different 

 morphological elements there can, thanks chiefly to the researches 

 of Wachsmuth and Springer, be no doubt. The question is : which 

 set represents the orals ? Wachsmuth and Springer believe that the 

 orals are represented by the proximals, but that these are often 

 resorbed, much as we know the orals to be resorbed in the ontogeny 

 of Anted.on. They believe that forms" with large proximals and 

 hidden deltoids are, phylogenotically, less advanced than those with 

 minute proximals and conspicuous deltoids. Euspirocrimis, for 

 instance, is more advanced than Cyathocrinus. Neumayr appears 

 to have believed that the deltoids were the orals and that the 

 proximals were modified ambulacrals. Unfortunately, reliance 

 upon the drawings of other authors led him to confuse the two 

 sets in some instances, so that his views were thought more unsound 

 than was really the case. 



For many years I have devoted considerable attention to this 

 matter, and have long believed the deltoids to be homologous with 

 the orals, and the proximals, when they exist, to be enlarged 

 ambulacrals. So great, however, was the opposition to this view 

 on the part of my departed friends, P. H. Carpenter and Charles 

 Wachsmuth, that in my published writings I always left the 

 question open and continued to amass evidence. I believe myself 

 to be now in a position to prove both these homologies definitely 

 and step by step. That, however, must be done in another place 

 with the help of adequate illustration. Here it is enough to point 

 out the great difiiculty of explaining the deltoids on any other 

 hypothesis (see p. 115 of the Monograph) ; also, one may draw 

 attention to the fact that the posterior deltoid and the posterior 

 oral stand in similar relations to the water-vascular system. 



The remaining elements of the tegmen are next discussed, and 

 a full history of the various opinions that have been held is given. 

 There are no new facts of importance, and no modification of 

 the views published by Wachsmuth and Springer in 1891, and 

 abstracted in the Geological Magazine for May of that year. 

 Details, however, are filled in, and this section with its accompanying 

 illustrations should be carefully studied. 



Following on this come some very controversial matters. The 

 ventral sac of the Fistulata "must not," we are told on p. 114, 

 " be confounded with the anal tube of the Camerata, which contains 

 simply the rectum." On the contrary, it " lodged a large portion of 

 the visceral mass," and " is generally composed of longitudinal i-ows of 

 hexagonal plates, which are often pitted at their sides, or perforated 

 by pores." These pores are supposed to have admitted water for 

 respiratory purposes. Messrs. Wachsmuth and Springer seem to 

 think it curious (p. 161) that in my earlier writings on crinoids 

 I should have regarded this supposed structure " as an excellent 



