ACEPHALES. 3G9 



side of it, and the combs are alike : the conical tcntacula liave their eyes at their external base : tht 

 siiles of tlie foot are garjiislied with a row of filaments. 



Emanjimila, Lam., lias exactly the same structure as Fissiirella ; but instead of a hole in the ape.t, its cloak and 

 shell have a little cleft or emargination on their anterior side, which also penetrates into the branchial cavity. The 

 nuirsins of the cloak envelope and in a great measure cover those of the shell : the eyes are on a tubercle at the 

 outer bases of the conical tentacula ; and the sides of the foot are as usual ornamented with filaments. 



Parmoplionis, Lam. (SculumMontt.)-Ks in Emarginula, the shell is covered, in a great measure, by the turned- 

 nii margins of the cloak: the branchia; and other organs are the same as in the two preceding genera; but the 

 oblong, slightly conical shell has neither hole nor emargination. [Sowerl)y unites this with the preceding genus.] 



THE NINTH ORDER OF THE GASTEROPODES. 



THE CYCLOBRANCHIATA.* 



These MoUusks have their hranchia; in the form of little leaflets or p5'ramids, attached iu a 

 circle, more or less complete, under the margins of the cloak, very nearly as in the Inferobran- 

 chiata, from which they are distingiushed by the nature of their hermaphroditism ; for, as in 

 the preceding order, they have no organs for copulation, and impregnate themselves. Their 

 heart does not emljrace the rectum, but varies in its position. We know only two genera, whose 

 shell never exhibits even a trace of a spire. 



The Limpets {Patella, Linn.) — 

 Have the body entirely covered with a conical shell ; and under the margins of their cloak there is a 

 circle of branchial leaflets. The anus and the orifice of the organs of generation are a little to the right 

 above the liead, to which there is a tliick, sliort proboscis, and two setaceous tentacula, having the eyes 

 at their exterior bases : tlie mouth is fleshy, and contains a [very long ribbon-like] spinous tongue, 

 winch is directed backwards, and lies folded deep within the interior of the body. The stomach is 

 membranous, and the intestine long, slender, and much convoluted. The heart is in front above the 

 neck, a little to the left. Some species occur in abundance on our sliores. 



The Chitons {Chiton, Linn.) — 

 Have a series of testaceous symmetrical plates set along the i>ack of their cloak, hut not oceupving 

 all its breadth. TJie margins of tlie cloak itself are coriaceous, either naked, or chagreencd, or gar- 

 nislied with spines, or hairs, or liundles of bristles. Beneath this margin, on each siile, is a row of 

 lamellated branchi.c ; and in front, a membranous veil over the moutli holds the place of tentacula. The 

 anus is under the posterior extremity. The heart is situated behind, upon the rectum. The stomach 

 is membranous, with a long convoluted intestine. The ovary lies above the other viscera, and appears 

 to open upon the sides by two oviducts. 



There are some small speceies on our sbores ; but in the seas of tropical countries they attain a much greater 

 size. (The Cli'itondtufi, Lam., distinguished by the valves being so small as only partially to cover the cloak, 

 should be re-united to Chiton, which, in the system of Blainville, forms a separate class, named Poli/plaxiphora, 

 and which, he supposes, leads the way to the Articulated Animals.) 



THE FOURTH CLASS OF MOLLUSCA. 



THE ACEPHALES.f 



The Acepliales have no apparent head, but a mouth only, concealed in the bottom, 

 or between the folds, of their cloak. The latter is almost always doubled in two, and 

 incloses the body as a book is inclosed between its covers ; but it frequently happens 



* In the system of Blninvillc ibe Cyclul)ruin;liiiita is an order tlmt to iliscover it, nor inticed to see iiiiy other origan of rcfipiratinn except 



embraces the l.loris. With the Inst three genera of the precedintj thftl of a eord of leaflets wliiuh encircles the body under the Diar^iins 



or.ler and witli the Patella, lie makes his order Ccrvico-brancttiiita, of the clofil;. 



diii.led into the Ks/'/err-j and BrrtJicAi/frfj: the Reiiferes are the t M. de Bhiinville unites my Acephnles and Braiichiopodes in one 



Till elite; for Ilc EU|iposes that they breathe by moans of a va.scultir class, his .-yivvj/ia/fij/iora, 

 network in the cavity situated ahovc the bead. 1 have not been able 



