M O L L U S C A. 



631 



oliuwt. ORLE I. 



The animals of this Order are all fixed to othsr 

 bodies, without the power of displacing themselves. 

 The branchial and anal openings are neither opposite, 

 DOT do they communicate directly with each other. 

 The branchial cavity is open at its upper extremity 

 only, and the aperture is fringed with tentacula; the 

 gills of both sides are continuous. The genera are 

 distributed into two sections. 



SECTION I. 



This contains the animals formerly included in the 

 genus Asciclia of Linna?us. They are distinguished 

 fay the separate or independent existence of the differ- 

 ent individuals. In some species many individuals 

 adhere to the rock in clusters, and appear to con. 

 titute one animal ; but these can be easily separated, 

 as they possess no common covering nor organical con- 

 nection. The genera of this section are four in num- 

 ber, and are distributed into two families. In the 

 first family the orifices are furnished with four rays, 

 and the genera are Boltenia and C'ynMia, the former 

 represented by the AtcidLa pedunculata, having the body 

 supported on a stem, while in the latter the body U ses- 

 sile, a* in C. conchilega, a native of the British seas. 



In the second family, the anal and branchial open- 

 ing* are either destitute of rays, or they exceed four 

 in number. The genera are two. In the Phaltiuia 

 the body is sessile. The branchial orifice usually pos- 

 sesses eight rays, and the anal one six. The P. men- 

 tula is very common on rocks and old oysters in the 

 British seas. The P. inteitiiialit and prunum are like- 

 wise native*. In the genus Clavelina the body is pe- 

 dunculated, and the apertures are destitute of rays. 

 The C. tetudiformit has been added to the British 

 Fauna by the industry of Dr. Leach. The genus Mam- 

 maria of Mullcr will probably constitute a third family 

 in this section, when its structure has been determined. 

 The body b smooth, having the base fixed to sea- 

 weeds, and the summit perforated by a single aperture. 

 One species, the M. mammilla, inhabits the British seas, 

 having been observed at Leith by Professor Jameson, 

 and at Belfast by Mr. Templeton. The genus Bipapil. 

 laria of Lamarck is involved in equal obscurity. 



SECTION II. 



In this section are included animals which were for- 

 merly placed among the zoophytes, and chiefly in 

 the genus Alcyonatm. They are compound animals, 

 many individuals being united under a common cover- 

 ing. They admit of division into three families. 



In the first family the branchial and anal orifices 

 have pix rays each. The genera of this family are 

 three in number. The Diaxona is distinguished by 

 the body being sessile, orbicular, and consisting of a 

 ingle system or group of individuals. The D. rio/a- 

 cea of Savigny is the only known species. In the 

 liu'cma the body is sessile and polymorphous, and the 

 individuals are arranged in systems or groups. The D. 

 variolosus first observed by Gartner is a native of our 

 eas, and is the Alcyonium ascidioides of Pallas. In 

 the .Sigiltina, the body is conical and pedunculated, 

 consisting of a single group of individuals. The S. 

 australis of Savigny is the only known species. 



In the second family the branchial orifice only has 

 six regular rays. The genus Synoicum has the body 

 cylindrical, vertical, and pedunculated with a single 

 system. The S. turgens of Phipps, a native of the 

 Arctic seas, U the only species which has been de- 

 2 



scribed. In the month of August 1817, we observed a Moiiusca. 

 Synoicum, adhering to a rock in the sea at the Isle of ~~Y~~~ 

 May. It differed from the lurgent, as described by 

 Savigny, chiefly in the smoothness of the skin. In the 

 Sydncum the body is inversely conical, vertical, peduncu- 

 lated, with a single system. The S. turbinatum ob- 

 served by Dr. Leach as a native, is the only known 

 species of the genus. In the genus Alpidium, the 

 body is variously shaped, sessile, consisting of many 

 systems, which are destitute of a central cavity. The 

 A.Jicut, or Alcyonium pulmonaria of Ellis's zoophytes, 

 belongs to this genus. In the Polyclinum the body is 

 likewise sessile, but the individuals are in systems with 

 central cavities. The Didemnum is sessile, spongy, 

 and incrusts other bodies. The anal opening is ob- 

 scure. 



In the third family, both the branchial and anal 

 orifices are destitute of rays. The body invests fuci 

 and rocks, and consists of several systems. In the 

 genus Euccelium, the systems are destitute of central 

 cavities. In the genus Bolryllus, on the other hand, 

 there in a central cavity to each system. The last 

 genus contains the following British species: B. 

 Lcachii, BorUutii, Sohlotteri, and Conglomeratic. 



OBDEB II. 



The animals which remain to be considered, as con- 

 stituting this order, are free, and float about in the wa- 

 ter. Many individuals are united, forming a conical 

 bag. The anal and branchial openings are diametri- 

 cally opposite to each other. The branchial cavity is 

 open at both ends, the anterior aperture is destitute of 

 tentacula, but furnished with a denticulated ring. The 

 bronchia- are disjoined. There is only one genus in 

 this order known, which has been termed Pyrosoma. 

 It contains the following species, verticillata, panicula- 

 la, and allanttcum. 



SUBDIVISION II. THALLIDES. ThallWct. 



This subdivision embraces animals whose inner tunic 

 adheres to the external one at all points ; whose bran- 

 chial orifice is furnished with a valve ; and whose bron- 

 chia? consist of two united narrow leaves. 



The animals here referred to were first formed into 

 a separate genus by Brown, in his History of' Jamaica, 

 under the title Thalia, a name now usurped by Flora. 

 Forskael afterwards instituted his genus Salpa, and Sir 

 Joseph Banks the Dagysa, for the reception of similar 

 animals. The name of Forskael has been preferred by 

 naturalists. Few of the species have been examined in 

 a recent state. They appear to be numerous, and to 

 exhibit a considerable variety of character; perhaps suf- 

 cicnt to warrant their distribution into several distinct 

 genera. They appear to inhabit chiefly the seas of 

 warm climates. 



CLASS VI. BRACHIOPODA. BHACHIO. 



This class was instituted by M. Cuvier, in conse- IODA ' 

 quence of an examination of the animal of the Patella 

 unguis of Linnams. Its characters are well marked, 

 and abundantly justify the propriety of the change. 

 The animals of this class are acephalous ; and, like the 

 conchifera, have the cloak divided into two lobes, pro- 

 tected by a bivalve shell. These lobes are free at the 

 anterior margin. The branchiae consist of small leaves, 

 arranged along the inside of the edge of the cloak, and 

 intimately united with it. From the body, between 

 the lobes of the cloak, issue two arms, fringed with 

 filaments. These are capable of folding up in a spiral 



