126 



Cuvier, and more especially of tlie genera Terebratula and Orbicula." 



The paper commences by a brief historj of the formation ofthe 

 order by Cuvier, and then refers to the anatomical particulars 

 which have been recorded as regarding Terebratula by prcceding 

 writers. Among these Palias seems to have given the best de- 

 scription of the animal. It is on one of this subdivisioti tliat the de- 

 scription given by Linnaeus of the animal of his genus Anonūa is 

 founded. 



Mr. Ovven's materials for the anatoniy of Terebratula consist of 

 specimens of four sppcies, three of which are inhabitants of the^ 

 South Pacific Ocean (including one brought home by Mr. Ciiming, 

 and tvvo by Captain P. P. King, R.N.jj the fourth, Ter. psittacea, 

 Brug., was brought from Felix Harbour, Boothia Peninsula, by 

 Comraander J. C. Ross, R. N, 

 "" The mantle adheres very closely to the valves : the Jobe which 

 corresponds to the perforated valve is traverscd Jongitudinally by 

 four large vessels ; the opposite lobe is similarly traversed by lwo 

 such vessels. Its margins are thickened, not as in the Lamellibran- 

 chiate Bimlves from contraction, but ovving to a peculiar structure 

 connected with respiration. They are piickered at regular distances, 

 the puckerings being apparently caused by the insertions of delicate 

 cilia, vvhich pass as far vvithin the mantle as they project out of it, 

 but which are so minute as to be observable only by means of a 

 lens. In the interspaces ofthe cilia the margin ofthe mantle is mi- 

 nutely fringed,and within the fringe isacanal, \vhich extendsalong 

 the whole circumference. From this canal the large vessels of 

 the mantle lobes take their origin : the}' may be regarded as the 

 branchial veins conveying the aerated blood to the tvvo hearts, 

 which are situated exterior to the liver, and just vvithin the origin 

 ofthe internal calcareousloop: they are accompanied in their course 

 by much smaller vessels, probably the branchial arteries. Such is 

 apparently the system of respiration in Terebratula. 



The viscera octupy a very small space near the hinge. The ali- 

 mentary canal commences bya small puckered mouth, situated im- 

 mediately behind thefolded extremities of thearms. It passes back- 

 vvards, and expands into a niembranous stomach, surrounded by the 

 liver, a bulky gland of a green colour and minute follicular tex- 

 ture, which communicates with it by many orifices. The intestine 

 passes dovvn to the hinge, and then turns to the right side and ter- 

 minates betvveen the tvvo m antį e- lobes. No trace of a salivary gland 

 was found. 



The generation of Terebratula is that of the ordinary Bivalves. 

 In tvvo ofthe larger specimens the ova had insinuated themselves 

 betvveen the layers of the mantle, and partly surrounded the 

 branchial vessels. When so far advanced they obscure the organi- 

 zation of the mantle vvhich adapts it for respiration : this organi- 

 zation is consequently most satisfactorily observed in very young 

 individuals. 



Mr. Ovven describes in detail the museles, the arms, and the pe- 

 culiar internal testaceous apparatus or loop connected with the 

 hinge and supporting the arms. In the species vvhich he examined, 

 with the exception of Ter. psittacea, he finds that the loop possesses 



