VOL. XXIV.] PHILOSOPHICAL TRANSACTIONS. ^OQ 



^n Account of Animals and Shells sent from Carolina to Mr. James Petiver, 



F. R. S, N°299, p. 1950. 



Among the crustaceous animals Mr. P. gives (Sect. I.) a description of the 

 5-holed Carolina, sea-urchin or fritter: echinus compressus Carol. &c. Musei 

 Nost. 125 fig. 



This is a very singular animal, having 5 oblong perforations through the body 

 of the shell, viz. 4 against as many points of a 5-rayed star, lying in the midst 

 of the shell; the other is placed between two of its beams: these are of different 

 magnitudes, having seen them from less than 2 inches to almost 4 diameter, and 

 this last, in the midst, where its thickness exceeds not half an inch, and gradually 

 to its edges, which are thinner than a shilling. 



He afterwards gives an account, in Sect. II. of several species of muscles, 

 cockles and other bivalves ; in Sect. III. of some patellae, cochleae, buccina and 

 other single shells ; and lastly, (Sect. IV.) of two glossopetrae ; viz. glossope- 

 tra Carol, maxima nigrescens ponderosa. This is one of the largest he ever 

 yet saw, being above three inches from the tip to the hollow or middle 

 of the root ; this last part is very large and protuberant : the teeth black, 

 and smooth on the edges, but in the middle much furrowed ; the whole very 

 weighty. 



Glossopetra Carolin. leviter serrata c nigro rubroque eleganter variegata. 

 This is almost a straight tooth, i. e. very little waving to either side, as 

 most of them more or less do ; its edges are rather pounced than notched, 

 from the tip to the middle of the root near an inch and half; its toothy 

 part is finely variegated with red and black. 



The Doctrine of Combinations and Alternations, Improved and Completed. By 

 Major Edward Thornycroft. N° 299, p. I96I. 



In order to understand what follows, it must be observed, 1st. That as in the 

 notation of powers, aaaabbbcc is designed by a*b^£^i and universally p times the 

 position of a, q times the position of b^ r times the position of c, by a^b^c^, 

 so in things exposed likewise : (unless where it is proposed they should be all 

 different) which indices, as they have here no relation to powers, but express 

 only the occurrences of those things to which they respectively belong, I there- 

 fore call indices of occurrences. 



2dly, That as often as I shall hereafter mention the combinations or alterna- 

 tions of the p*, q\.r^, or 5% which considered by themselves are capable of no 

 variation, I mean of those things whose indices they are. 



VOL. v. E K 



