312 Scientific Notices — Zoology. [AiPRii, 



Ft. In. 



Height to the tip of the horn 10 4 



Do. to the point of the spines of the dorsal vertebrse .... 6 6 



Length of the spine 10 10 



Distance between the extreme tips of the horns measured 



by the skull 11 10 



Distance between the tips measured in a strait line across 9 2 



Length of each horn 5 9 



(Dublin Philosophical Journal.) 



8. Pecten iiiveits, a new Species. 



It having been suggested, in hasty terms, in the number of 

 the Annals of Philosophy for November last, that the Pecten 

 niveus, described in vol. xiii.p. 166, of the PhilosophicalJournal, 

 is perhaps a mere variety of P. islandicus, I judge it expedient 

 to institute a comparison between the two species after the man- 

 ner in which I have compared P. niveus with P. variiis, the only 

 species to which it approaches in its characters. P. islandicus 

 Las from 70 to 100 or more* ribs ; P. niveus has invariably 46 ; f 

 in the J'or?ner, the ribs are very irregularly grouped from 2 to 6 

 being crowded together, with smaller ones intervening, but 

 without any regularity ; in the latter, they are beautifully regu- 

 lar ; in P. islandicus they are marked with very numerous, deli- 

 cate, erect laminae, or scales, without any appearance of echina- 

 tions ; in P. niveus they are compact and smooth, with scattered 

 echinations toward the margin of the shells ; P. islandicus is a 

 tolerably thick shell, of a pale-reddish colour, with concentric 

 circles of a deeper tint; P. niveus is a very thin shell, of a pure 

 white colour ; P. islandicus has a margin singularly irregular in 

 its teeth, recalling the idea of that sort of leaf which is termed 

 Jolium crispatnm ; P. niveus has its marginal teeth as regular as 

 those of a Cockle. If after this P. islandicvs and P. niveus 

 should be considered identical, then assuredly P. maximus and 

 P.jacobaus are so also ; and scarcely any two species of a genus 

 can be named, that must not, on the same grounds, be mere 

 varieties. I now subjoin the distinctive characters of the three 

 species. P. islandicus, testa suborbiculari rubente, fasciis con- 

 centricis saturatioribus, radiis circiter 100 varie aggregatis 

 rotundati.s lamellulis densissimis scabriusculis. P. niveus, testa 

 orbiculari, fragili Candida, radiis 46 subcompressis rotundatis 

 sparsim breviter tenuiterque echinatis. P. varius, testa orbicu- 

 lato-oblongii, colore varia, radiis 32, obsolete squamosis, sub- 

 compressis, rotundato-planatis, sparsim crasse echinatis. W. M'G. 

 — (Edin. Phil. Jour.) 



* In a specimen in the Museum of the University of Edinburgh, the number is 104 ; 

 in a very perfect specimen belonging to W. Nicol, Esq. Edinburgh, the number is 106, 

 •f- That is to say in 32 specimens. 



