216 REPORT 1851. 



ever, it becomes a steering and a sculling-machine. Nephthys progresses in 

 water by throwing its body into a rapidly succeeding series of the most ele- 

 gant undulations, maintaining at the same time a steady position of the head, 

 advancing prettily like a fairy-wave through the fluid. 



The Annelids grouped under the Cuvierian genus of Ariciadm are little 

 known. In the sj'stematic portion of this Report, it will be seen that the 

 author has succeeded in multiplying this genus by the addition of several 

 iindescribed species. The body of Aricia Ctivieri is distinguished into two 

 distinct portions, one of M'hich, the cephalic or anterior, is characterized by 

 the absence of branchias, the presence of a double row of setiferous processes 

 on either of the dorsal aspects of the body, and of short conical cirri beneath 

 each ventral foot. This segment of the body is prominently annulated, and 

 vigorously muscular. It exceeds in diameter very much the posterior ; it is 

 the true motive apparatus of the worm. The posterior two- thirds of the 

 body is apparently motionless and lifeless, and scarcely at all capable of 

 voluntary motion. To this region the branchial organs are exclusively 

 limited. The setae of the inferior feet are of a bright mother-of-pearl ap- 

 pearance, strong (figs. 43, 44), short and curved ; they are carved on one 

 side in a very peculiar mannei*. This sculptured work can only be described 

 as resembling scales laid transversely one over another imbricately, each 

 scale being strengthened by a minute " corpus " on the mid-point of its free 

 edge. This variety, it is obvious from the structure, is designed for pushing. 

 The setae of the other feet are flat, blade-like, and unserrated in their edges. 

 The brushes of setae in the vicinity of the head are sessile, those near the 

 feet are pedunculate. Placed on the dorsal aspect of the body, the ventral 

 being smooth, it is easy to understand the manner and mechanism of loco- 

 motion. The soil is preparatorily channelled by the fore-part of the body, 

 expressly constructed for such description of work. Through the gallery 

 thus formed the posterior and passive moiety of the worm is slowly urged 

 along by the mechanical operation of the setiferous feet, which are dorsally 

 placed for this purpose. In this memoir, for the first time, several new 

 species of Aricia will be described, presenting the generic characteristic of 

 closely approximated ' rings ' at the oesophageal portion of the body. Within 

 the limits of this portion each segmental ring is furnished with four strong 

 setiferous feet, the posterior part of the body being intestiniform and desti- 

 tute of branchiae. In another species the posterior four-fifths of the body is 

 provided with ridges armed with three rows of stalked hooks. 



The appendages in the Opheliadce assume a new character ; they are 

 short fleshy threads attached to either side of the body, and chiefly to the 

 two posterior thirds. Ciirhatidns Lamarckii is the culminating perfection 

 of this type of structure. In this worm, elegant only for its long, wavy, 

 bright red and filiform appendages, the setiferous feet are thrown into abey- 

 ance. Frequenting concealed passages, under stones resting almost always 

 on a clayey soil, the presence of these worms can only be discovered by ob- 

 serving in the vacuity the tangled webs of red threads which seem gifted 

 with the power of independent voluntary motion ; these are at once motive 

 and branchial appendages. This worm seems to enjoy very little power of 

 locomotion. It rolls and coils itself in a self-emitted slime, if withdrawn 

 from its native habitat. It is furnished on the under surface of the body 

 with two rows of strong curved blunt spines, as if specifically intended for 

 walking or creeping. At some little distance on the side of the same seg- 

 ment, is observed another row of setae, much exceeding the former in length 

 and differing from them in structure, being only long, slightly curved and 

 flattened hairs ; they are well calculated to aid in progression by pane- 



