REVIEWS — CANADIAN ORGANIC REMAINS. 45 



relations to recent crinoids — that the lateral aperture usually regarded 

 as the ovarian orifice, was the true mouth* ; and he supports his 

 opinion by a train <of argument not easily to be set aside. The series 

 of small triangular valves with which the orifice in question is provid- 

 ed in many species, may be looked upon as the homologues of the 

 *'lips" or buccal apparatus of the living Pentacrinus (P. ca'put 

 MedtiscB) of the West Indian seas. 



In his section on the Lower Silurian species of Canadian cystidese, 

 Mr. Billings describes nineteen new forms, belonging to his genera, 

 Pleurocystites, Grlyptocystites, Comarocystites, Amygdalocystites, 

 Malocystites, Palseoeystites, and Ateleocystites. The genue Pleuro- 

 cystites is a very remarkable one. It is chiefly characterised by the 

 dissimilar structure of the two sides of the body ; a series of com- 

 paratively large plates covering the dorsal side, whilst the ventral 

 side consists of an open space protected by an integument covered 

 with numerous small plates. The genus, with us, appears to range 

 from the Chazy to the Hudson Eiver group ; and geographically from 

 Canada to Wales (Caradoc group), and Bohemia (Barrande's efa^e 

 D.) Six species are enumerated : P. squamosus (plates plane or 

 slightly concave ; pectinated rhombs, with obtuse angle above) ; P. 

 roiustus ? (plates concave) ; P. JiUtextus (pectinated rhombs with 

 acute angle above ; plates on ventral side fewer and larger than in 

 P. squamosus) ; P. elegans ; P. exornatus ; and P. Anticostiensis 

 (plates probably smooth) . P. elegans and P. ornatus may perhaps 

 prove eventually to be mere varieties of P. filitextus. The genus 

 Grlyptocystites is characterised chiefly by its cylindrical body, en- 

 closed in four series of plates (= 4 basal +5 + 5 + 5), some with 

 re-entering angles ; and by the presence of ten or more pectinated 

 rhombs, a strikingly peculiar character. It ranges from the Chazy 

 to the Trenton group, and comprises the following species : G. 

 multiporus (arms 4+1, extending down the sides of the body); 

 G. Logani (plates with stellar ridges, arms not developed : Trenton) : 

 G. gracilis ; G. Porhesi (plates large and strong, with numerous 

 ridges and striae : Chazy). Of the genus Comarocystites only one 

 species, O. punctatus, has been recognised. It occurs in the Trenton 

 group, and may be readily distinguished by its deeply-concave 

 plates. The basal plates are three in number, succeeded by from 



* Except in the genus Malocystites (Billings), in which the apical orifice is regarded as 

 the mouth. 



