GASTEROPODA TECTIBRANCHIATA. 



3.55 



'^#"— - 



Fig;. 1C9. — :iurifctella Lcachii. 



The Bursatellks, Blainv., — 



The lateral crests are united in front, so as only to leave 

 an oval opening for the water to pass to the branchiae 

 which are also destitute of a covering cloak. It is, how- 

 ever, probable that this genus should be allowed to lapse 

 into the Notarchus.* 



The Aceres, (Akera, Muller) — 

 Have the branchiae covered like the preceding genera, but 

 their tentacula are so much shortened, widened, and sepa- 

 rated, that there seems to be none at all, or rather they 

 form together a large, fleshy, and nearly square buckler, 

 under which the eyes are placed. Moreover, their her- 

 maphroditism, the position of their sexual organs, the 

 complexity and structure of the stomach, the purple liquid 

 which several of them shed, all approximate them to the 

 Aplysise. The shell, in such as have one, is more or less 

 convolute, with a slight obliquity, without a visible spire, 

 and the mou h has neither sinus nor canal; but as the 

 columella is convex and protuberant, the mouth has a 

 crescent-like shape, and the part opposite to the spire is always widest and rounded. When the shell 

 is buried in the cloak, M. de Lamarck names the genus Bullaea. The shell has few whorls, and is too 

 small to contain the animal. 



The Hull,,-,, aperta, Lam., is an example which is found in almost every sea, where 

 it lives on oozy bottoms. When the shell is [external], covered with a thin epidermis 

 and sufficiently roomy, M. de Lamarck allows them to retain the old name Bulla. 

 The Bulla lignaria, ampulla, and Iit/dalis are examples, [distinguished not only by the 

 characters of the shells, but by peculiarities in the armature of the stomach, which 

 ts of two or three comparatively large osseous pieces or jaws of different shapes 

 in each. Of those of B. lignaria, Gioeni constituted a genus to which he assigned Fi «- 170.-b u ii*. aperta. 



his own name ; it is the Tricla of Retzius, the Char of 

 Bruguiere, and disfigured our systems until the cheat 

 was detected by Draparnaud.] I restrict the term Accra 

 to such species as have no shell whatever, or merely a 

 vestige of it behind, although the cloak lias the external 

 form of one. The genus is the Doriilium of Meckel 

 and Lobaria, Blainv. There is a small species in the 

 Fig. 171 — Bulla lignaria. Fig. 172.— B. ampulla. Mediterranean (Bulla carnisa, Cuv.), whose stomach 



is as destitute of any armature as its cloak is of a shell, but the oesophagus is flesh; and very thick. 



The Gasteropteron, Meckel, — 

 A]. [.ears to be only an Aceres with the sides of the foot expanded into broad fins, by whose aid it is 

 enabled to swim, which it does in a reversed position. It also has no shell, and 110 Stony apparatus 

 in the stomach. A very slight fold of the skin is the sole vestige of a branchial cover to he observed. 



The one species known (6. MeckelU) is a Mediterranean Mollusk, about an inch long; by two in breadth, when 

 its winus are spread out. 



Until a mor- ample anatomy has been made of it, we believe that it is in this order, and near to the 

 PleurobranchUB, that the singular genus 



Umhki.ii a, Lain. {Gastroplax, Blainv.) — 

 Should he placed. The animal is a great circular Mollusk, whose foot exceeds by niueh the cloak, and 



has its upper surface roughened with tubercles. The viscera are in a superior ami central rounded 

 part. The eloak is only visible by its slightl] projecting sharp edge along the entire front, and on the 

 light Bide, Under this slight edging of the cloak are the branchiae, in lamellated pyramids, Like ile.se 

 ,,i Pleurobranchus ; and behind them is a tubular anus. Under this same margin, in front, are two 



. .),,/....,/ wtrMU, Mootac;., rabid to a genu, bj Oktn ander i!.<- eoTti ib« b« ■ uil lh« raperioi in " ■ ander «»• ' 



. ;, i. •,! lull aaarl] allied • Hmtda eraaeulai network, .o that lb< iruc position of la la Ben io 



of aiiao, ri & u * »«•*' ally oi Apljala, bat from want Placobraackoa.] 



ul a knowledge ol the brmnchjai, I canaol clutlfy It. [The braiichitr 



