PECTINARIA. 245 



wards, thin, brittle, and arenaceous, composed of equal grains of 

 sand neatly cemented together, and smooth on both the exterior and 

 interior surfaces ; the apertures circular, with an even thin rim. A 

 specimen that measured 1 6'" was 4'" in diameter at the anterior, and 

 3'" at the posterior aperture. 



The description given by Pallas of this worm is inimitably excel- 

 lent. Amongst other things he tells us that the tube stands im- 

 mersed in the sand in a perpendicular position ; and indeed the worm 

 is very helpless when it is laid horizontally. When at ease, and 

 covered with the water, it protrudes from the wide aperture of the 

 tube, the head with its four cirri, the comb of bristles, and its many 

 tentacles. The latter are in continual movement ; they are short- 

 ened and lengthened, and twisted about at will, in search seemingly 

 for fit grains of sand ; and as the grains adhere, by a gluten secreted 

 from the surface, they are carried within reach of the other organs, 

 by means of which the worm applies them to the rim of its tube, 

 and thus carries the structure upwards. The tube is only increased 

 by addition to this end ; the posterior is plugged with the abdominal 

 appendage, and undergoes no material alteration*. The size of the 

 tube corresponds exactly to that of the worm ; and the animal can 

 withdraw within it for shelter. It can also turn itself in the tube so 

 as to alter the relation of the back and venter to the sides of the 

 case. This, according to Pallas, never exceeds 2^ inches in length ; 

 but Sir J. G. Dalyell has seen a specimen from Shetland 5 inches 

 long, with a tenant " 4^ inches in length, by about J of an inch at 

 the shoulder." It is not unlikely that this giant was the representa- 

 tive of a different species. 



The Pectinaria nuricoma of Blainville (Diet, des Sc. nat. Ivii. 436, 

 Atlas, f. 1) is also distinct, and may be distinguished by the pos- 

 terior cirrus being bifid at the point, and longer than the anterior 

 cirrus, and by the feet being equally distanced. 



(a) South Devon, G. Montagu. 



2. P. grannlata, front obliquely truncate, the space behind the 

 spines rugose; marginal tentacula very short; abdomen spathu- 

 late, pointed at the end. — Tube slender, tapered posteriorly and 

 curved. 



Sabella granulata, Linn. Syst. 1268. 



Amphitrite auricoma. Mull. Zool. Dan. Prod. 216; Zool. Dan. i. 26. 



tab. 26. 

 Pectinaria auricoma, Grube, Fam. Annel. 82. 



Hab. The coralline region. 



Obs. As might be inferred from an inspection of the tube, this 

 worm is more slender and quickly tapered than the P. belgica. 

 Other distinguishing marks are expressed in the specific character. 



* " This creature constructs a very delicate tube, as thin as paper, exclusively 

 of the grains of sand agglutinated together in an extraordinary manner. The 

 thickness of the side does not exceed a single grain, each lies in its proper place. 



