OASTEROI'olM 11 TBROPODA. 49 



G. Mfr/w/ii : Rosso, Di*s. de Pteropodum Ordinc, Hake, 

 J813, f. 1113; and JJlainv. Malacol.. pi. xlv, f. 5; or Clio 



timitti, Delle Chiaie, M.-inor., pi. ii, f. 18. A small animal an 

 inch long, and two broad, tin- \vinLf-. being extended. From the 

 Mediterranean. 



For the present, and until our anatomical studies are more ex- 

 tended, we arc under the neees.sity of placing in tliis order of Tecti- 

 bran -Itiat i. \\\\ I even very cloee t> tin- pleurobranchus, the singular 

 genus, 



GASTBOPLAXj Jt/fiiiir. ( )M r,i;i :i.i.i>. of Lam. 



'I'll.- animal is a lug.- and circular niollusca, whose foot projects con- 

 siderably beyond tin- mantle, and its upper surface is studded with 

 tubercles. The viscera are in a round, superior, and central part. 

 Tin- mantle is only visibl.- by its slightly projecting and trenchant 

 nlges, alon.uf the whole of the front and of the right side. The lamel- 

 1 ite.l pyramidal branchiae, like those of the Pleurobranchus, are under 

 this slight ni irgin, and behind them is a tubular anus. Under this 

 HUM margin and forwards, are two tentacula, longitudinally cleft, as 

 in I'leurobranclms, at whose internal base are the eyes; between 

 them is a kind of proboscis, which may possibly be the organ of 

 ration. There is a large concave space in the anterior margin of 

 th toot, the edges of which are susceptible of being drawn up like the 

 mouth of a purse, and at the bottom of which is a tubercle, pierced 

 by an orifice, which perhaps is the mouth, and surmounted by a 

 fringed membrane. The inferior surface of the foot is smooth, and 

 serves the animal to crawl on, as in the other Gasteropoda. 



The animal carries a shell which is stony, flat, irregularly rounded, 



thickest in the middle, with trenchant edges, and marked with slightly 



ntiic striae. It was at first thought to be attached to the foot, 



but more recent observation has proved that it is on the mantle, and 



in the usual place*. 



ORDER V. 



HETEROPODA, Lam\. 



The Heteropoda are distinguished from all other mollusca by 



In tin- spri-iim-n from the UritMi Museum described by M. de BlainviUe, 



lluili-t. 1'hil., isp.j. p. 17-, ; 1>\ the name of GA8TROPLAX, the slu-H is, in fact, 



.-.I to tlu- mi. k-r pan i.f tin- foot, ami by what means it is difficult to determine ; 



tin- tiKintli. lm\M-\-r. is so thin, that it M-rms as if it must have been protected by 



; yimml li.is ju-,t brought to France a specimen which hail lost its 



. it ;ipp<;u>, ti-iu-es of the membranes which attached it to the 



mantle can be p , lir whii-ii, no remains of muscles are visible. 



l;u- -lu-ll isaNo found in the Mediterranean; its animal, however, has not yet 



; IMT\;-C|. 



..ily of the HKTEROPODA, which he names NBC- 



MA, and unitt-s tlu m in hi- ordt-r of the NUCLEOBRANC IIIATA with another 

 family that !u- calls PTKROIO.)\. an 1 which, of all my Pteropoda, only includes the 

 II ' i.c Argonaut* with it, on account of some conjecture, of which 



ignorant. 



rot, in. 



