SPIRORBIS PAGENSTECHERT. 399 
5. SPIRORBIS PAGENSTECHERI, De Quatrefages, 1865. Plate CXX XVII, fig. 23—collar-bristle. 
Specific Characters.—Collar normal. Branchiz normal. Operculum shaped like a shako, 
with a circular calcareous plate distally, and acts as a brood-pouch. Body with three anterior 
and from eight to twelve setigerous segments posteriorly. Collar-bristles somewhat genicu- 
late, with a differentiation at the base, the web having finer serrations than those which 
follow on the blade; or without a differentiation, the blade being a simple serrate (geniculate) 
process. Bristles of the third series have some serrate sickle-shaped forms. 
Anterior hooks of the normal shape, with about twenty minute teeth along the anterior . 
border. The main fang is somewhat short and blunt. The tube is abundant on Zostera 
at Naples, is dextral and pure white, with a ridge along the summit of the last coil. The 
aperture is circular. 
SYNONYMS. 
1863. Spirorbis spirillum, Pagenstecher. Zeitschr. f. wiss. Zool., Bd. xii, p. 486, Taf. xxxvill et xxxix. 
1865. 5 Pagenstecheri, De Quatrefages. Annel., t. i, p. 491. 
1868. 5 Pr Claparéde and Mecznikow. GZeitschr. f. wiss. Zool., Bd. xix, p. 37, 
IaH, SOMy ye, Z 
3 - rr Claparéde. Ann. Neap., p. 443. 
1875. ‘ . Panceri. Atti Soc. Ital. Sc. Nat., vol. xviu, p. 535. 
1893. 5 * Lo Bianco. Atti Accad. Sci. Napoli, vol. v, p. 92. 
1897. = es. Caullery and Mesnil. Bull. Sc. Fr. et Belg., t. xxx, p. 201, fig. 8a—b. 
1917. - i Rioja. Anél. Polig. Cantab., p. 82. 
Habitat—-Probably on the southern coast, and as S. pusilloides in Blacksod Bay 
(Southern). 
Elsewhere it occurs at Naples (Claparéede) ; between Cette and Agde (Pagenstecher) ; 
Shores of Cantabria (Rioja) ; Isles of Gambia (Fauvel). 
Pagenstecher! (1863) found a species between Cette and Agde on seaweeds and shells 
which he thought was Spirorbis spiridllum, but as afterwards shown by De Quatrefages, it 
belongs to a different species (S. Pagenstechert, De Quatrefages). He recognised the herma- 
phrodite condition, the ova being present in the anterior region of the abdomen and the 
sperms in the posterior ; whilst the development of the eggs took place in the brood-pouch— 
with the disc-like operculum on its extremity. He studied the development of the eggs in 
March, the form of the early larva with its prostomium and two lateral lobes, the large 
body-segment and its caudal lobe, and the various later stages to the secretion of the tube 
with its transverse lines. Four eyes appear in the free larva, two smaller in front, and two 
larger behind—ncarly in a line with the collar-bristles ; whilst i front are the branchie as 
simple lobes ; im the centre of the body is the reddish-brown gut and three pairs of lateral 
bristles. The great breadth of the anterior region, like that of certain Terebratulids, is striking 
in the third stage, and the appearance of two translucent ovoid bladder-like bodies on each 
side of the gut anteriorly is also noteworthy in this and later stages, the last having four 
branchiz on each side with filaments and pinne, an operculum on the right side, four eyes, 
and four pairs of bristles, the collar-bristle being figured in a recognisable condition. The 
first bristles to appear are the lateral, the collar bristles beg developed when the lateral 
are present. 
1 “Zeitschr. f. wiss. Zool.,’ Bd. xu, p. 486, laf. xxxvili and xxxix. 
