of the British Shreios. 33 



all those noticed by different authors shall have had their dentitions 

 examined with reference to the three types indicated by Duvernoy. 

 Our most common species, the so-called S. araneus, which, as be- 

 fore stated, unquestionably belongs to the second of the above types 

 {Hydrosorex,) I have little doubt is synonymous with the S. tetra- 

 goniirus, the only other noticed by Duvernoy under that section, be- 

 sides the true S. fodiens of Pallas and himself, from which it is 

 clearly different. M. Duvernoy has given a description of this spe- 

 cies, as well as a coloured representation of the entire animal, and 

 though this last may appear at first sight larger than our araneus, 

 as well as slightly different in some other respects, yet it accords ex- 

 actly with specimens of a rather unusual size obtained by me from 

 the fens of Cambridgeshire, to which I shall have occasion to refer 

 presently. His description is for the most part of a relative na- 

 ture serving to distinguish the S. letragonurus from the *S'. fodiens. 

 Hence it will not admit of direct application where we have not the 

 last-named species with which to contrast it. But so far as it can 

 be judged of, it would seem to favour the opinion I have above ha- 

 zarded. Thus he observes that it is distinguished, in the first place, 

 by its much smaller size ; secondly, by the form of the snout, which 

 is narrower and more elongated ; thirdly, by the form of its feet, 

 which are less thick and less broad than those of the S. fodiens. 

 Lastly, he notices some slight differences in the teeth compared with 

 those of the species just mentioned. One of these consists in the 

 first denticle on the margin of the lower middle incisor being so 

 little removed from the point of that tooth as to appear but as a 

 lobe of this last, and to give in consequence to the extremity of the 

 tooth a bilobated character. Another difference consists in the den- 

 ticle of the second lateral incisor in the lower jaw being less de- 

 veloped. With respect to the last two peculiarities, of the former 

 it is not easy to judge without knowing its appearance in the S.fo- 

 diens, but I conceive it will be hardly thought inapplicable to our 

 species, in which I have already noticed (when describing its den- 

 tition) three denticles arranged in a series behind the main point of 

 the tooth in question, to which last the first is sufficiently approxi- 

 mated to convey the appearance above alluded to by Duvernoy. To 

 the latter, — the rudimentary state of the second point in the second 

 lateral incisor below, — I have in like manner already drawn atten- 

 tion. 



M. Duvernoy assigns the following dimensions to the S. tetra^ 

 gonurus : 



VOL. II. NO. 7. C 



