OCR Text |
Show 434 MOLLUSCA. THEOIDEA, Def. The pedicle seems to have been incorporated with the small valve(l). 0RBICULA, Cuv. The Orbiculre have two unequal valves, one of which, that is round and conical, when viewed by itself, resembles the shell of a Pa. tella. the other is flat and fixed to a rock. The arms of the animal, -C;iopus, Poll,-are ciliated and spirally recurved like that of the Lingulre. The seas of Europe produce a small species, Patella anomala, Miill., Zool. Dan. V, 26; Jlnomia turbinata, Poli, XXX, 15; Brett. Sowerb., Lin. Trans., XIII, pl. xxvi, f. 1. The DxsoiNlR, Lam., are Orbiculre, the inferior valve of which is marked by a fissure. The CRANIA, Brug. Should be approximated to the Orbiculre. The arms of the animal are also ciliated, but the shells have deep and round internal museu· lar impressions, that have caused it to be compared to the figure of a skull. One of them inhabits European seas; .llnomia craniolaris, L.; or Craniu personata, Bret., Sowerb., Lin. Trans., XIII, pl. xxv, f. 3. Several are fossil; such as the Gran. antiqua, and the others of which M. Hreninghaus has given an excellent Mono· graph. (1) Thecidea mediterranea, Risso, Hist. Nat. de la Fr. Merid., IV, f.183;-Th. radiata, Fauj. Mont. de StPierre, pl. xxvii, f. 8. Further and more precise ob· servations are requisite to enable us to class the MAGA.S of Sowerby, the STRI&O· c:RPRAL.A. of Defrance, and some other neighbouring groups. 435 CLASS VI. CIRRHOPODA(l )· [LEP As and TRITON, Lin. J The Cirrhopoda, in several points of view, are intermediate between this division and that of the Articulata. Enveloped by a mantle, and testaceous pieces which frequently resemble those seen in several of the Acephala, their mouths are furnished with lateral jaws, and the abdomen with filaments named cirri, arranged in pairs, composed of a multitude of little ciliated articulations, and corresponding to a sort of feet or fins similar to those observed under the tail of several of the Crustacea. Their heart is situated in the dorsal region; and the branchire on the sides ; the nervous system forms a series of ganglions on the abdomen. These cirri, however, may be considered as analogous to the articulated appendages of certain species of Teredo; while the ganglions in some respects are mere repetitions of the posterior ganglion of the bivalves. The position of these animals in the shell is such, that the mouth is at the bottom and the cirri near the orifice. Between the last two cirri is a long fleshy tube, that has sometimes, but erroneously, been taken for their proboscis, and at the base of which, near the back, is the opening of the anus. Internally, (1) M. Delamarck has changed this name into CmnrPEDA, making it a class. M. de nlainville also makes a class of them, but he changes the name to NEMATO· Pon.t, and places them with the Chitones, in what he calls his type of the MJ.LEN· TOZA.l\IA, |