HETEROCIRRUS ATER. 



259 



ventrally. So far as the structure of the body-wall goes, this form closely approaches 



Dodecaceria. 



1. Heterocirrus atbr, De Quatrefages, 1865. Plate CVTI, fig. 8 — 8 b — bristle and 



hook. 



Specific characters. — Head cylindrical, rounded in front, numerous small eyes in a 

 band on each lateral region sloping from within outward and forward about the middle of 

 the head. First four body-segments are short and bear pale green branchiae. The buccal 

 segment carries the large, long grooved tentacles and a branchia immediately above and 

 behind. The next four segments have branchise on the dorsum. Body 1 to 2 in. 

 long, rounded in front, flattened posteriorly ; the caudal region being oar-shaped, and 

 rather abruptly narrowed to two papilla at the tip, with the anus between. Colour dark 

 blackish-green. Behind the tentacles are indications of five segments, four bearing 



OTTt. 



TVC. 



Fig. 127. — Transverse section of Heterocirrus ater, De Quatrefages, from Guernsey. Oc. 2, obj. a. 



capillary bristles dorsally and ventrally. At the seventh segment the characteristic 

 crotchets occur in both dorsal and ventral divisions. Each crotchet has a shaft dilating 

 from the base upward a short distance, then remaining of nearly equal diameter to the 

 neck where it bends backward and again forward at the tip, which in certain views shows 

 a median rib and two expanded lateral areas, but in lateral view it resembles an old 

 snuff-spoon. Toward the tip of the tail these crotchets are of great proportional strength. 



Synonyms. 

 1841. Nereis sextentaculata, Delle Chiaje. Descrizione, Tav. cy, fig. 16. 

 1865. Heterocirrus ater, De Quatrefages. Aiinel., i, p. 465, pi. x, figs. 13 — 17. 

 1894. „ „ De St. Joseph. Aim. Sc. nat., 7 e ser., t. xvii, p. 52. 



1911. Dodecaceria ater, Mcintosh. Ami. Nat. Hist., ser. 8, vol. vii, p. 158. 



Habitat. — Abundant in the thick coating of Lithothamnion covering the gneiss rocks 

 at low water, and in the cracks of rocks in long galleries, bent in various ways — though 

 generally doubled — in Guernsey and Herm. Shores of France (De Quatrefages, etc.). 



Head rather elongated like that of Phyllodoce, slightly tapered and smoothly rounded 

 m front, and with two dark patches of minute eyes on the dorso-lateral region of its 

 middle, the snout in front of them often being pale in the preparations, whilst that behind 



