MOLLUSCA — CLASS II. BRACHIOPODA. 177 



arms to the cirrous tentacula of those animals ; they differ, however, in 

 not being articulated, and their relation altogether with the Lepades is 

 one of very remote analogy. Cuvier distinguished them as a new and 

 separate class, but still arranged next in order to the Lepades. Lamarck 

 places them at the end of his " Conchiferes Monomyaires," merely 

 as a family of that order. Professor Owen and Deshayes both consider 

 that they are entitled to take the rank of an order ; the latter author 

 moreover admits that there is far less affinity between the Brachiopoda 

 and the rest of the acephalous mollusks than there is between the 

 acknowledged divisions of Bimuscular and Unimuscular. In accordance 

 with our own candid opinion, and at the suggestion of Deshayes, we have 

 adopted the still higher rank assigned to them by Cuvier, and we follow 

 Lamarck in placing them after the Tropiopoda, upon the presumption 

 that their branchial apparatus presents a modification of structure inter- 

 mediate between that of the proximate classes. 



The animal may be described as being of an ovate or oblong form, 

 always contained within a bivalve shell ; it is furnished with two long 

 spirally-twisted ciliated arms, as also several muscles, and the mouth is 

 central, but there is no head, or eyes. The abdominal viscera are small, 

 protected on each side by the lobes of the mantle. The branchiae are 

 vascular and symmetrical, springing up within the soft texture of the 

 mantle. 



The shell is either horny or calcareous, and always bivalve ; it has no 

 hinge ligament, but adheres strongly to the animal by attachment of the 

 muscles ; it is also fixed externally either by a long pedicle or short 

 fibrous tendon, or immediately by the lower valve. 



The Brachiopoda, which are not very numerous, are divided into two 

 families according to their mode of attachment ; we propose to call them 

 as follows : 



Tendinosa. 

 Adh^erentia. 



VOL. I. 



2 A 



