2 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 39. 



DESCRIPTIONS OF GENUS AND SPECIES. 

 Genus ARENICOLA Lamarck. 



The characters of this genus may be stated thus: Polychseta, 

 usually found burrowing in sand or gravel, of elongate cylindrical 

 form, provided with pairs of dorsally-borne branched gills which, 

 however, are not present on the first seven segments. Prostomium 

 small, bounded posteriorly by the nuchal groove, without tentacles 

 and palps. Peristomium without cirri. Each chgetigerous segment, 

 except the first three or four, is subdivided into five annuli; the 

 annulus which bears the parapodia is larger than the others. Each 

 parapodium consists of a conical notopodium, bearing capillary 

 setse, and a neuropodium, in the form of a muscular pad or ridge on 

 the lateral or ventro-lateral region of the chretigerous annulus, trav- 

 ersed by a deep groove in which a row of crotchets is situated. The 

 pharynx has no armature except a series of papillse the tips of which 

 may be capped with chitin. One or more pairs of glandular coeca 

 are present on the posterior part of the oesophagus; a short distance 

 posterior to these is a pair of hearts. The number of nephridia 

 varies in different species, five, six, or thirteen pairs being present; 

 the first nephridium opens on the fourth or fifth segment. Coelomic 

 septa have disappeared in the region of the body in which the stomach 

 is situated, but septa are constantly present at the anterior border 

 of the first, third, and fourth chsetigerous segments and also in a 

 greater or less extent of the intestinal region of the worm. In all 

 the known species, except A. claparedii Levinsen, there is a pair of 

 statocysts (otocysts) in the peristomium. 



The genus Arenicola is divisible into two sections, one, the caudate 

 section, containing those species in which a posterior region or " tail" 

 is present upon which neither parapodia nor gills are borne, the other, 

 the ecaudate section, comprising those species in which the para- 

 podia, and generally also the gills, extend to the posterior end of the 

 animal. 



Up to the present no specimen belonging to the ecaudate section 

 of the genus has been recorded from America. The two species, 

 A. ecaudata Johnston and A. gruhii Claparede, which comprise this 

 section, therefore, claim little attention in this communication. It 

 may be stated for the guidance of workers on the American littoral 

 fauna that these two species have hitherto been found, for instance, 

 in Great Britain and France, near low-tide mark and chiefly in coarse 

 gravelly sand, among stones or in debris at the base of rocks formed 

 by the breaking down of the latter. The burrows of these worms 

 are oblique or sinuous cavities in the gravel or between the rocks 

 and the castings of the worms are composed of coarse material, hav- 

 ing little coherence, and therefore soon falling to pieces. The well- 



