386 SPIRORBIS. 
dextral and tube sinistral. Caullery and Mesnil state that all dextral forms have the oper- 
culum on the right side and all sinistral on the left. Bush, again, considers it improbable 
that any species could turn in both directions. An abridged table, partly applicable to the 
British species, 1s appended :— 
Four pairs of ;/Fourth setigerous 
bristle - tufts| segment with} Collar bristles with spinous web and gap _‘S.. cancellatus, Fabr. 
on thorax) dorsal bristles. 
(sub. - gen. Page SEERORS) 
| 
Paradexio-| segment without 
spura). dorsal bristles. 
Tube dextral The ee bristled 
thoracic seg- 
Collar bristles without the gap. . 8. violaceus, Fabr. 
Ten to six- 
teen abdo- 
minal 
segments. | 
Collar bristles | | Cygeneutienin ( 
without the | saucer- 
gap. } shaped. 
magmis (Gulb- Tube. S. spirillum, L. 
gen. ae | 
sptra). HKm- 
bryos incuha- 
ted in— 
( No sickle-shaped bristles {Collar bristles ) 
Ojgareulinin. ( in third bristle-tuft. | without gap. | Srcommugatus Mont: 
Talon of oper- ( Collar bristles 
Collar bristles | culum with- with fine S. borealis, Daud. 
-. , .}/Threebristle-+ with gap, Tube. > out protu- serrations 
Ahuloe gums tufts on incubation | berances ex- ( Coarse serra- ) 8S. mediterraneus, 
thorax. in— | ternally. tions ) Caull. & Mes. 
Operculum. Helmet-like. S. militaris, Clap. 
Miss Bush (1908) made an important contribution to the subject of the Spirorbids in 
her volume on the Tubicolous Annelids from the Pacific. She relied much on the opercula 
and the collar-bristles, the hooks being less fully dealt with. She gives a brief historical 
summary of the group, including many features of interest. She poimts out various modifica- 
tions of the operculum, which often pushes forward several plates, and is of opinion that a 
new calcareous plate may be developed or renewed on the same side as before. In her review 
the following forms have the embryos developed in the tube, viz., S. sprrorbis, L., S. spirillum, 
L., and S. asperatus, Bush; whilst in S. granulatus, L., S. validus, Verrill, S. Stempsonc, Verrill, 
and S. quadrangularis, Stimpson, there is opercular development. She found in the opercular 
embryos of various species, such as her Spirorbis abnormis, S. granulatus (2?) and S. validus, 
a white patch which split under pressure into short rods which dissolved in acid. She thought 
this a calcareous substance ready for secreting the tubes, or that the mass would enable them 
to sink rapidly, both views, however, being doubtful. She states that in S. spirorbis strings 
of embryos with well-formed sete have been found on the dorsum, having apparently passed 
from an opening in the body-cavity behind the thorax. This differs from the condition in 
Britain. She discards the classifications of both De St. Joseph and Caullery and Mesnil, 
and prefers to arrange the species according to the structure of the bristles of the collar, 
and the structure of these bristles is certainly of great importance. 
A. In the forms having the distinct fin-like base there are differences; the serrations 
on the edge of the blade are fine, and the spines on the basal fin coarser. In Sp. borealis, 
Daud., the type-species, there are three to five odd sete in the third anterior fascicle 
with sickle-shaped fringed edges. 
B. The serrations on the edge of the fin and of the blade are coarse. Ex. Sp. 
militaris. ; 
c. The form with the rounded fin gives rise to those in which the fin is defined by 
a more or less definite notch, which entirely disappears, forming simple tapered blades. 
Ex. Sp. Pagenstechert and Sp. pusillus. 
