CURRENT LITERATURE. 25 



As a resiilt of tlie investigation, the author confirms the view that 

 ctenidial filaments, held together by ciliated discs, are of essentially simpler 

 structure than those connected by subfilamentar tissue, and the ciliated 

 disc is a more archaic mode of junction than the cellular connection. 



It is proposed to abolish the group Pseudolamellibranchia, to remove 

 Pinna from the Aviculidae and place it in a separate family, the Pinnidae, 

 and to include it, and the Ostreidae and Limidae, in the Eulamellibranchia. 

 The remaining Aviculidae, together with the Pectinidae, Spond!jlidae,an(\ 

 Dimyidae, are to be joined to the Filibranchia,and to constitute a new group 

 theKleutherorhabda. With regard to the Septibranchia, Dr. iridewootl does 

 not consider there is sufficient evidence to warrant their removal from the 

 Eulamellibrancliia, as a separate order, and consequently he places them 

 as a sub-order (Poromyacea), and unites them with the remaining Lamelli- 

 branchia into one order, which he proposes to term Synaptorhabda. 



The following is an outline of Dr. Ridewood's classification :^ 



(1) Order Protobranchia. — This is Pelseneer's order adopted with- 



out alteration. 



(2) Order Eleutherorhabda. — Arranged in series on the two sides 



of the gill axis are elongated filaments. Adjacent filaments 

 are held in position l)y stifi" cilia disposed in isolated patches 

 (ciliated discs). 

 It comprises tlie sub-orders Dimyacea, Mytilacea, and Pectinacea. 



(.''>) Order Synaptorhabda. — There are no ciliated discs. The 

 interlamellar edges of adjacent filaments are connected by 

 cellular tissue. These organic interfilamentar junctions are 

 situated at uniform intervals up the filaments, and convert 

 the linear interfilamentar spaces into series of fenestrae. 



This order comprises the sub-orders Ostracea, Submytilacea, 

 Tellinacea, A>neracea, Cardiacea, Myacea, Pholadacea, 

 Anatinacea, and Poromyacea. 



Dr. Eidewood recognises that the amount of family disruption this 

 scheme involves will doubtless prove startling to the systematist,andhe does 

 not claim that it represents in any way the genetic affinities of the forms 

 included. What he aims at, is the '" formation of classificatory tables, admit- 

 tedly artificial and based each on a single character, .so that the taxonomist of 

 the future may, by a process of correlation of these tables and a careful 

 weighing of the respective values of the facts therein laid before him in a 

 compact and readily assimilable form, arrive at the truth concerning the 

 phylogenetic history of the Lamellibranchia."' The present work is intended 

 as a contribution towards this ultimate object. 



The remainder of the paper, and comprising the bulk of it, consists of a 

 minute survey of gill-structure throughout the Lamellibranchia and is 

 accompanied by numerous figures ; appended to it, is a very full biblio- 

 graphy which seems to contain references to all the literature bearing upon 

 the morphology of Lamellibranch gills. 



The paper is indeed one of the most important contributions the subject 

 has yet received, and is one which will serve as a basis for research'in years 

 to come. — A. D. Imms. 



