602 PHILOSOPHY OF ZOOLOGY. 



b. Shell discoid and spiral. 



In this group there are at least four genera, with well 

 marked characters exhibited by the shell. 1. Magilus, 

 (MQNTFORT). The shell posteriorly is fixed, with regular 

 spires, the last of which is produced into a tube. The 

 animal is unknown. M. antiquus. The Serpula recta an- 

 fractibus tribus contiguis regulariter involutis, and Ser- 

 pula recta umbilico pervio anfractu apicis unico involute 

 of WALKER *, either belong 1o this genus, or deserve a se- 

 parate place. 2. Spirorbis. Spires discoid, not produced 

 into a straight tube, and dextral. S. communis, spirillum^ 

 granulatuS) carinatus, corrugatus and corneus, are na- 

 tives. 3. Heterodisca. Like the preceding, but the spires 

 are sinistral. H. heterostrophus, sinistrorsus, minutus, co- 

 nicus, lucidus and reversus, are natives. 4. Lobatula. 

 Discoid, with the tube divided into numerous unequal cells. 

 L. Jar eta and concamerata, described by MONTAGU as 

 Serpulae, are native examples. In the genera Serpula, Ver- 

 milia and Spirorbis, the branchiae constitute a tuft of fan- 

 shaped filaments, on each side the mouth. 



f d Tribe. 



Body destitute of a shell. 



A. Branchiae external. 



1. Furnished with antenna. This division includes the 

 Linnean genera Aphrodita and Nereis, now formed in- 

 to numerous genera, which LAMARK distributes into the 

 following families. 1. Aphrodita, including Aphrodita f, 

 Halithea, Palmyia and Polynoe. 2. Nereides, including 

 Lycoris, Nephtys, Glycera, Hesione, Phyllodoce, Syllis, 

 Spio and Diplotis. & EimictC) including Leodice, Lysi- 



* Testaeea Almtsla Rariora, p. 3. Tab. f. II, 12. 



^ The structure of the aerating organs in this genua are exhibited by 

 Sk E. Home, Phil. Trans, 1815, tab. xiii. 



