398 SPIRORBIS PUSILLOIDES. 
three thoracic segments. Two nephridia debouching by a single aperture in the median 
Ime behind the branchiz. Collar-bristles without a step beyond the basal web, the third 
series having two bristles with curved and serrated tips. The following bristles are said 
to be large and sickle-shaped (De St. Joseph). Hooks of the two posterior thoracic segments 
resembling those of Spirorbis borealis. Ova (few) in the anterior abdominal segments, those 
behind containing sperms. Developed in the operculum. 
SYNONYMS. 
1837. ? Spirorbis pusilla, Rathke. Fauna de Kryn, p. 117; Mém. l’Acad. St. Petersb., i, p. 407. 
1864. Spirorbis pusilla, Grube. Insel Lussin., p. 92. 
1880. a Pagenstechert, Langerhans. Zeitschr. f. wiss. Zool., Bd. xxxiv, p. 123, Taf. v, fig. 42. 
1894. Mera pusilla, De St. Joseph. Ann. Se. nat., 7° sér., xvi, p. 351, pl. xin, figs. 3888—392. 
1897. Spirorbis pusillus, Caullery and Mesnil. Bull. Se. Fr. et Belg., t. xxx, p. 202, fig. p, p. 190. 
1905. a pusilloides, Bush. Tubic. Annel., pp. 250, 254, 255, 260, 261 and 267. 
- ane Pagenstecheri, idem. Ibid., pp. 254, 255, 257, 258, 260, 261, 265. 
1912. ee pusilloides, Pixell. Proc. Zool. Soc. Lond., p. 797, pl. Ixxxviu, figs. 9a and 9b. 
1914. a Southern. Proc. Roy. Irish Acad., vol. xxxi, No. 47, p. 148. 
1915. " 5 idem. Irish Se. Invest., No. 3, p. 49. 
Habitat.—Clare Island and Blacksod Bay on shells of Mytilus and Trochus (Southern). 
St. Vaast ; Arcachon, on oysters (De St. Joseph) ; on Lithothamnion, and on Purpura 
at St. Vaast-la-Hougue (Caullery and Mesnil); Madetra—Teneriffe, on algee (Langerhans) ; 
British Columbia (Pixell). 
Tube 1 mm. in diameter, fragile, in a nautiloid spiral, with a central umbilicus and three 
whorls. 
In his original description of Sprorbis pusilla, Rathke gives two coils to the tube, with 
its longitudinal keel, like the S. carinata of Lamarck. This form may be a variety of 
S. pagenstechert. He found it on mussels and the blades of Fuci. 
A single example of the last species, viz., Spirorbis pusilloides, Rathke and De St. 
Joseph, kindly sent by Mr. Southern, has alone been under examination, and the collar- 
bristles in this instance had no gap above the web, and might pass for those of S. spardlium. 
Mr. Southern, however, states that he has seen all intermediate forms between this and the 
typical one with the differentiation at the base of the blade. Caullery and Mesnil also 
found a simple geniculate condition of the collar-bristles in preparations forwarded by 
Baron De St. Joseph. Whether the violet pigment on the gut of S. Pagenstechert and the 
red on S. pusilloides denotes more than variation is uncertain. The species was first 
described by H. Rathke and later by De St. Joseph under the name of Mera pusilla, 
but Miss Bush,? seeing that the specific name was used by Rathke in 1836 for a species 
from the Black Sea, proposed the present title. It chiefly occurs on shells of oysters, though 
Southern found it on mussels and Trochi. There remains doubt as to the connection of this 
form with that described by Rathke, and as to its relationship with Spororbis Pagenstecherr. 
Both develop eggs in the operculum, and in all probability S. pusillovdes is a variety of the 
other. The single preparation unfortunately was so injured that no hooks could be observed. 
1 «Ann. Sc. nat., 7° sér., t. xvii, p. 351, pl. xiii, figs. 888—392. 
* ¢Tubicolous Annelids from the Pacific’? (Harriman Alaska Hxped.), 1908, p. 250. 
