336 Mr. J. Blackwall on some new species 



were present, and I believe that no species of Teredo is without 

 them. 



The plugging up of the terminal volutions in Aporrhdis and 

 other Gasteropoda, and the consequent withdrawal of the poste- 

 rior parts of the animal, are analogous to this operation in Te- 

 redo ; the same principle excites the action in both cases, self-pre- 

 servation. 



It will be observed that the alliance of Teredo with Fholas, 

 through the apophysary processes, is more decisive than between 

 any two other bivalve families. I trust that I shall not be con- 

 sidered fanciful if I venture to remark, that there are points of 

 analogy between Teredo and Dentalium so striking as almost to 

 give some weight to the idea that it forms the passage to the 

 Gasteropoda ; in support of these views I beg malacologists to 

 observe the similar vermiform character of the animals, the at- 

 tachment of their posterior parts to the shells by sphincteroid 

 muscles, the peculiar plan of the admission of the water by short 

 siphons in conjunction with the sphincter, the single branchial 

 dorsal lamina on each side, their separation from the body, and 

 other minor analogies. These concordances almost make me 

 think my hypothetical surmises have some foundation, and that 

 the transfer of Pholas and Teredo, &c., from the bottom to the 

 top of the scale of the bivalves, would not be an injudicious pro- 

 cedure. 



I conclude by apologizing for the unreasonable draught I have 

 made on the valuable pages of the ' Annals.^ 



I am. Gentlemen, your most obedient servant, 



William Clark. 



XXIX. — Descriptions of some newly discovered Species and Cha- 

 racters of a new genus 0/ Araneidea. By John Blackwall, 

 F L S 



Tribe OCTONOCULINA. 



Family Salticid^. 

 Genus Salticus, Latr. 

 1. Salticus obscurus. 



Length of the male ^th of an inch ; length of the cephalo- 

 thorax y^^ ; breadth -^-^ ; breadth of the abdomen y^ ; length of 

 a posterior leg ^ ; length of a leg of the third pair y'g . 



Cephalo- thorax large and nearly quadrilateral, projecting a 

 little beyond the base of the falces*, which are small, conical 



* The organs of spiders improperly denominated mandibles, as they are 

 situated above the labrum, and, consequently, form no part of the oral ap- 

 paratus, I have proposed to n&me falces. 



