474 Mr. W. Clark on the Classification of the 



Limnea between it and Cyclostoma is unavoidable, as it would be 

 inconvenient to place them in the direct branch of the Conovuli ; 

 we have nevertheless kept the free-air-breathing animals together 

 at the head of each branch, with the exception of Otina, which 

 may perhaps prove a pulmonifer. I must here observe that 

 Natui-e has put a veto on any arrangement that shall be exempt 

 from anomalies and incongruities ; we must look at her largely 

 as a class, with a few well-marked divisions, and not be too sen- 

 sitive about Utopian details of strict natural order. AVe might 

 have placed the Hermaphrodite Pleurobranchidse, Pteropodidse, 

 Aplysiadse, Bulhdse, Helicid^ and Conovulidse, to follow the in- 

 operculated Muricidse and Cyprgeadse; but we think the union of 

 these families with proboscidal animals, and of distinct sexes, 

 would be more removed from a natural arrangement than the 

 plan we have submitted, and which we are prepared to expect will 

 follow the fate of every other system of classification that has pre- 

 ceded it, however great may be the authorities from which they 

 have sprung. It is universally admitted that the most accre- 

 dited plans are unsatisfactory, and I venture to predict, that to 

 the end of time our successors will make the same remarks. In 

 short we cannot accomplish an arrangement which Nature her- 

 self has not created. 



Analysis of the Synopsis. 



First Division. '' 



Acephala palliobranchiata. , 



I have removed this section of the Acephala from its position 

 at the head of the bivalves, to which I think it has no preten- 

 sions. I consider it a distinct inferior group forming the passage 

 from the Ascidiae andCirripoda to the Acephala lamellibranchiata ; 

 by its pallial branchiae it has close relations with Ascidiae, and 

 with the Cirripoda through the long convoluted cilial buccal ap- 

 pendages, which, though not articulated, in consequence of ad- 

 vanced animality, still prove its connection with that tribe. If 

 the Palliobranchiata have the sexes distinct, as some authors have 

 stated, the position I now place them in, with the strict herma- 

 phrodite Acephala, would not be correct, and in harmony with 

 my sexual distribution ; but I believe that these views of bisexu- 

 ality in the bivalves are eri'oneous, and the causes that have led 

 to them are those mentioned in the anatomy of Pholas dactylus 

 under the head of the " reproductive organs." 

 , The Brachiopoda are very rare British productions : I have only 

 met on the southern coasts with the minute Megathijrk cistcUula, 

 but the Te^:iibratida caput serpentis and the Cmfija a^nomala have 



