NAINEREIS QUADBICUSPIDA. 517 



mence on one of the twenty anterior segments, but are rudimentary anteriorly, and 

 gradually increase. In the Levinsenians they begin on the fourth setigerous segment and 

 only occur on a certain number of anterior segments, whereas in the Ariciidae they extend 

 to the posterior end, and their insertion is more dorsal than in the Levinsenians, which, 

 moreover, have more simple feet, with a dorsal and a ventral cirrus, though the latter is 

 often absent. The bristles are not annulated in the Levinsenians. They have three 

 anal cirri, whereas the Ariciidge have two or four. The proboscis is less complex than in 

 the Ariciiclas and there is no oesophageal caecum. The ventral nervous system is intra- 

 epidermic, whereas in the Ariciidae it is intra-coelomic. 



Mesnil and Caullery 1 place Theodisea under the sub-genus Nainereis, Blv., of the 

 genus Aricia, And. and Edw. They enter T. anserina, Clap., Port Vendres; T. liriostoma, 

 Clap., Naples; T. mamillata, Cun. and Ramage (Claparede ?). In this group the 

 prostomium is rounded. Lo Bianco puts Nainereis as a synonym of Theodisea. 



It is understood that Dr. Eisig is at present engaged with the Ariciidae, and is of 

 opinion that the genus Theodisea of Fritz Miiller is unnecessary, and that the old genus 

 Nainereis {Naidonereis of others) including N. quadricuspidata, seems to be sufficient for 

 the known forms. 



1. Nainereis quadricuspida, Fabricius, 1780. Plate LXV, figs. 5 and 5 a — head; Plate 

 LXXXVI, figs. 2-2 b— bristles ; Plate LXXXVII, figs. 5-5 b— feet. 



Specific Characters. — Head forming a rounded button-shaped process set on the 

 peristomial segment, which is notched at each side. Body about 3 ins. in length, slightly 

 tapered in front and considerably diminished towards the tail, which ends in two rounded 

 dorsal papillae and two short ventral cirri. Anterior region of thirteen bristled segments. 

 Branchiae commence on the sixth foot and continue of comparatively large size till the 

 eighth or tenth segment from the tip of the tail. At the tenth foot the branchia is 

 flattened and acutely lanceolate, and it is separated by a space from the dorsal division 

 of the foot, which bears a fan-like tuft of tapering bristles with smooth shafts and spinose 

 tips. The dorsal cirrus behind has an enlarged base and gently tapered tip. After an 

 interval the slightly convex and long inferior division occurs, with a prominent blunt lobe 

 or papilla rather below its middle posteriorly, and directed inward and backward. A 

 dense series of the strong and slightly brownish, curved (club-shaped) bristles occupies 

 the whole length of the division, with a few tapering serrated forms amongst them. 

 Most of the short, strong forms show distinct serrations towards the curve. The ventral 

 division ends in a notch ventrally. 



After the change in the structure of the foot occurs, as at the twenty -third, the 

 slightly tapered dorsal cirrus has in front of it a group of long tapering bristles with 

 smooth shafts and serrated tips, and a few bifid forms— all supported by four spines. A 

 low rounded papilla closely adjoining the foregoing represents the inferior division with 

 two spines and a few slender serrated bristles. Posteriorly a ventral cirrus appears 

 beneath the division. 



1 ' Bullet. Scientif. de la France et de Belgique/ Tom. xxxi, 4 e ser., ii, 1898, p. 143. 



