196 FLOEENCE BUCHANAN. 



Systematic Description. 



Family Spionidse. 



Hekaterobranchus/ gen. n. 



Spio quadricornis. Lam., *^Anim. s. Vert./ vol. v, p. 319.^ 

 A single pair of dorsal branchise, situated on the 1st seg- 

 ment, and very large. 



no trace whatever of a lumen in them, and consequently none of external or 

 internal openings. In Haplobranchus there are the same pigmented organs 

 of unknown function on the bases of the branchiae, in some specimens at 

 least, as are described and figured by Mecznikow in Fabricia (' Zeit. f. wiss. 

 Zool.,' vol. XV, p. 331, and pi. xxiv, fig. 8). Can tliese represent the pro- 

 stomial ciliated pits from which Meyer considers (vol. viii, pp. 629 — 634) the 

 most anterior portion of the common median duct to the exterior of the 

 modified thoracic nephridia of Serpulids is to be derived? They open 

 separately to the exterior on either side beneath the collar. Mecznikow does 

 not say whether the common aperture to the exterior of the pair of nephridia 

 he describes in the 2ud segment is on the prostomium or not. 



I will also mention that there is a sinus round the intestine in Haplo- 

 branchus, as Dr. Bourne suggests there may be. In the anterior region I 

 cannot in my sections see the dorsal vessel he mentions. The alimentary 

 canal nearly touches the body-wall dorsally. The coelom, however, in this 

 region is divided into distinct longitudinal cavities, four, or more anteriorly, 

 two, on each side. 



My sections would also seem to show that Haplobranchus has an evertible 

 pharynx, which, when inverted, reaches back into the 2nd segment. But 

 further investigation is needed. 



' "EKarepog = each (singly) of two. The name is meant to imply that two 

 kinds of branchial organs are present, and that there is one single pair of 

 each kind. 



- I have identified this form with the Spio quadricornis of Lamarck, 

 because it with its four horn-like tentacles (tentacles proper and branchia3) is 

 exceedingly suggestive of the name — much more so than the animal — Spio 

 crenaticornis figured by Montague, to which Lamarck refers. (Lamarck 

 refers to it as "Diplotus hyalina" because Montague's figures are wrongly 

 numbered, but according to the text the figures 6 and 7 of pi. xiv ('Trans. 

 Linnaian Soc.,' xi) should be marked as Spio crenaticornis.) It is ex- 

 tremely probable that Lamarck saw Hekaterobranchus, and gave the name 

 "Spio quadricornis" to it ; and that he wrongly identified it with Spio 

 crenaticornis, Montague, which was probably also not a Spio at all, 

 but a Leucodore. 



