DENTALIADJE. 447 



distinction, presents some remarkable features in important 

 parts of its organisation. In the following summary of 

 the characters of Dentalium, we have adopted the views of 

 Mr. Clark, the more willingly since they appear to us to 

 get rid of some anomalies recorded to exist in its structure, 

 which rendered the creature's affinities extremely dubious. 

 The most essential differences between the two accounts 

 relate to the respiratory and circulatory organs, and to the 

 position of the vent. According to Deshayes, the branchiae 

 are grouped in the form of two tufts of long soft filaments 

 with clavate extremities, one on each side of the animal's 

 neck. According to Mr. Clark, on the other hand, the 

 branchiae are " two symmetrical, sublateral, and somewhat 

 post-centrally situated organs, having their bases fixed on, 

 and hanging from, the concave surfaces of the animal, with 

 their points vertically parallel to the bases ; they are 

 united at their inner surfaces by a bridle of branchial 

 strands arranged symmetrically. 11 The latter observer 

 finds the heart at the anterior end of the branchial cavity, 

 and holds this peculiarity of position of that organ to have 

 relation to the fact that the water, in this genus, flows to 

 the branchiae by the posterior aperture instead of in front. 

 The organs taken for branchiae by Deshayes, are regarded 

 by Clark as salivary glands, and the branchiae of Clark are 

 the lobes of the liver for Deshayes. As there appears to 

 be a distinct liver in a more usual position, and as the 

 relation of the circulation to the branchiae has been clearly 

 made out by the English naturalist, the usually accepted 

 view of the " cirrho-branchiate " character of Dentaliwm 

 becomes untenable. According to Deshayes, the vent in 

 this genus is anomalous in position among the Gasteropods, 

 being posterior ; Clark finds the vent at the base of the 

 branchial cavity, under the mantle, about the middle of 



