Zoological Society. 211 



ticulars with that of the Lingulce previously described by Cuvier ;. 

 subject, however, to certain modifications arising from the different 

 situations they inhabit. The Lingulce, which are provided with a 

 long pedicle, commonly live near the surface, and are found at low 

 water, partially buried in the sand for the protection of their fragile 

 shells against the violence of the tides ; the Terebratulce, on the con- 

 trary, are found in deep water, attached in clusters to fragments of 

 rocks and corallines by a bunch of short fibrous tendons issuing 

 through an orifice in the shell. 



" The essential points in which these animals differ from other 

 Bivalve Mollusks are as follow : — First, in the position of the soft 

 parts within the shell : in the Brachiopoda the dorsal part of the 

 visceral mass is against one valve, and the ventral part against the 

 other ; whilst in most of the Tropiopoda the back is placed directly 

 against the hinge, and the sides against each valve. Secondly, in 

 being provided with a pair of retractile brachia or arms : in the 

 place usually occupied by the branchiae, are two long spirally twisted 

 arms, generally more or less fringed, and so strongly resembling 

 in some species the branchiae of the Tropiopoda, that they were 

 at one time thought to be the true organs of respiration. These 

 retractile arms are said to be in constant activity for the purpose of 

 producing an inward current of water for the capture of animalculae, 

 and other alimentary prey. Thirdly, in the arrangement and posi- 

 tion of the branchiae : instead of the organs of respiration being di- 

 stinctly formed in lateral lamellae upon the body, as in the Lamelli- 

 branchiate Tropiopoda, they consist of a number of beautiful veins 

 and arteries incorporated within the substance of the two lobes of 

 the mantle. The calcifying organ of the Brachiopoda therefore has 

 a double function : in addition to its usual property of secreting the 

 calcareous mucus for the formation of the shell, it is made subser- 

 vient to the circulation of the aerated water. Prof. Owen observes, 

 ' that in this profuse distribution of vessels over a plain membra- 

 naceous surface, we perceive the simplest construction of the water - 

 breathing organ, presenting a beautiful analogy with the elementary 

 forms of the air-breathing organ in the pulmoniferous Gasteropoda' 

 In consequence of this new arrangement of the respiratory system, 

 the title of the Brachiopoda has been changed by De Blainville for 

 that of the Palliobranchiata, or mantle-breathing Mollusca. The 

 muscular system in these animals appears to be most complex ; the 

 Lingulce and Orbiculce are provided with three pairs of muscles, and 

 the Terebratulce have four. The large muscles are destined to open 

 and close the shell in the absence of a hinge ligament ; and the 

 small ones assist in sliding one valve over the other for the admis- 

 sion of water. 



" Until within the last few years only one species of Lingula was 

 known, and previous to the publication of Cuvier's memoir, before 

 alluded to, the shell of this singular animal gave rise to much specu- 

 lation amongst naturalists. Linnaeus, upon the discovery of an odd 

 valve of Lingula exhibiting no trace of any hinge ligament, described 

 it as a Patella. Both Ilumphius and Favanne took it to be the 



P2 



