Reviews — Geological Survey of Canada. 563 



Llandovery group. The fossils of the Arisaig rocks (Upper Silurian) 

 include descrij)tions of twenty new species, referred to Orthonota, 

 Goniophora, Grammysia, and a new genus Pteronitella, differing in 

 the arrangement of the hinge-structure from Avicula and Pterinea. 



Many of the genera of the older PaltBozoic bivalves require careful 

 reconsideration, in order to establish more well-defined characters, 

 and this Mr. Billings partly expresses as regards Orthonota, San- 

 guinoUtes, and Goniophora, which seem to be closely related to each 

 other, so that references to these genera must be regarded as merely 

 provisional. 



The notes on the structure of the Crinoidea and allied families 

 may be considered as the most important contribution to this volume, 

 and although published in the American Journal of Science for 

 1869-70, and in the Annals of Natural History, 1870-71, are repro- 

 duced here as part of the Survey Avork. The subject is one to which 

 Mr. Billings has given considerable attention, both in the Decades 

 1, 3, 4, of Canadian Organic Eemains, 1858-9, and other publications. 

 Considerable difference of opinion has arisen among palaeontologists 

 who have studied the subject, as to the position of the oral, anal, and 

 ambulacral apertures in the Palaeozoic Crinoids, Mr. Billings retain- 

 ing the opinions he expressed three years ago, and are embodied in the 

 present article without alteration, which comprises the position of 

 the mouth in relation to the ambulacral system, the structure of 

 Codaster, Pentremites, and Nucleocrinus, on the theory that the 

 ambulacral and ovarian orifices are the oral apertures, and other 

 points bearing on the question, to which are added some corrections 

 and additions. In this section, after alluding to Prof. J. Muller's 

 observations on the structure of the existing Crinoid, Antedon 

 EuropcBUS, Mr. Billings sums up : 



"It is said that the orifice, in the Cystidea and fossil Crinoids, which I believe 

 to have been both oral and anal in function, is anatomically identical with the 

 anus of existing Crinoids. If this be true, and if my theory is correct, it must 

 follow that the Cystidea took in their food through the anus. The same pheno- 

 menon has been observed in an immature Star- fish. In the earlier stages of growth 

 of Asteracanthion berylimis. Prof. A. Agassiz finds that there is, at first, only a 

 single opening in the digestive sac. This opening is both mouth and anus. After- 

 wards a second opening is formed, which is the permanent mouth. The other 

 opening thus becomes the anus. This Star-fish, therefore, in its embryonic stage 

 takes in its nourishment through the anus. In this respect it is a Cystidean. I 

 am informed the same arrangement occurs also in the Ophiurians and Echini. 

 Granting, therefore, that the valvular orifice of the Cystidea is the anatomical 

 homologue of the anal tube of a Pentacrhius, it does not follow it was exclusively 

 anal in its function. I, however, do not admit it to be the homologue of the anus 

 of Pentacrhtus. I believe it to be the mouth. Mr. Billings further states that in 

 the Echinodermata the position of the various organs, in relation to each other, 

 and also to the general mass of the body, is subject to very great fluctuations. 

 Thus, the mouth and vent are separated in some of the groups, but united in others ; 

 while either or both may open out to the surface directly upward, or downward, 

 or at any lateral point. The ovaries may be either dorsal or ventral, internal or 

 external, and associated with either the mouth, the anus, or with neither. The 

 ambulacral skeleton may be imbedded into and form a portion of the general 

 covering of the body, or lie upon the surface, or borne upon free moving arms. 



' ' Again, ( i ) the aperture which, in an embryonic Echinoderm, is both mouth 

 and anus, may in the mature stage become the anus only, a new mouth being 

 formed in another part of the body. (2) It may become the permanent mouth. 



