c A n i;o N i i i: nous A(. i. .;, 



more or less (loop marginal slit or sinus, near the middle, at the termina- 

 tion of a revolving band usually seen on all the \\lmrK: sinus sometimes 

 closed, excepting at interval^, so as to leave a series of isolated openings 

 in tho revolving hand. 



Tin- animal of the- Upical genus (I'lmrotomaria) of this extensive, and interest- 

 ing family, n<i\v so nearly extinct, has not, we believe, been ill x-rilx-d. That of 

 S-'i^in-ill't, however, an existing genus apparently related to this family (though 

 its shell is not pearly within), has been studied by Mr. Lucas Barrett, who describes 

 it as follows: "Tentacles long, serrate, at the base of which arc placed the eyes; 

 foot furnished with two pointed lappets, and two long, slender, serrated cirrhi on 

 each side. Opercnlnm \ery thin, ovate, with an obscure, snbspirul nucleus. No 

 part of the animal was external to the shell. The only living specimen occurred 

 at llammerfest, in torn -MX fathoms of water." 



The family PleurotumnriUlaB was represented during the Palaeozoic and several 

 later epochs, by a great number of beautiful shells, presenting elegantly sculptured 

 surfaces. It seems to stand, as it were, between the Trochula: and the Hnltuiiiln , 

 though authors are not agreed in regard to its relations to these and some of the 

 allied groups. It includes the genera Pleurotomaria, Plalyachitma, Sdsfnirella? 

 Miti-<'/iixi,niti, Trocltotoma, and Polytremaria. The Palaeozoic groups &uoayAaln 

 (as typified by such forms as E. jpentangulatiis, Sowcrby), Sralitcs, 7i'rr/;/<tWwiia, 

 l/i/!i-tina, and some undcscribcd genera from the older rocks, seem also to be 

 related to this family. 



Genus PLEUROTOMAIIIA, DEFRAJJCE. 



Sy*m. Anatomut [V.], MOSTTOBT, Conch. 8ytl. II, 1810, p. 278. 



1'leurolomaria, DsrBAXCK, Diet. Sci. Nat. XLI, 1826, 381. MEBKI, Sjrnon. 1828; and ib. 1830, 55. D- 



M.AYB8, Kncyc. Meth. Ill, Ub. 1830; and ib. 1832; 780. 

 Ktym. vxiufa, side ; TI/UM, to cat. 

 Examp. Pteurotomaria Quoyana, FWCUEB. 



Shell trochiform, or more or less- conical, pearly within, and variable in thickm -^ 

 according to the species, with or without an umbilicus; volutions angular, flat- 

 tened or rounded. Surface variously ornamented with stria?, nodes, granulations 

 or carina?. Aperture subquadrate, semi-oval, suborbicular or subrhombic ; inner 

 lip usually thin ; fissure of outer lip generally narrow and deep ; revolving baud 

 corresponding in breadth with the sinus. 



The shells included in this genus arc very similar in form, and the possession of 

 a fissured lip, to those of the recent genus Scismirella, but differ in size and tex- 

 ture all the known species of ScissureUa being minute, non-perlaceous shells. 

 The Pleurotomarias also closely resemble the genus Analomu*, of Montfort, from 

 which Ilormannsen and some others think they arc not distinct. Other authors 

 regard SciasnrrUa, D'Orbigny, and Anatomits, of Montfort, as synonymous. Judg- 

 ing from Montfort's description of the genus Anatomus, however, it seems scarcely 

 possible that it can be identical with ScitmtreUa, since he distinctly states that 

 the typical species of his genus is a pearly shell, and that the animal is without 



