472 PKOF. E. EAT LANKESTEE ON GOLFINGIA MACINTOSHII. 



system. There are no special respiratory organs. A pair of nephridial sacs (rarely 

 only one) are always present and always (?) have an internal aperture. The reproductive 

 organs lie in the form of transverse ridges at the base of the ventrally attached pair 

 of retractor-muscles (of the introvert) ; the eggs have numerous pore-canals in their 

 chorion ; sexes distinct. Free or living in shells or tubes. In all seas. 



Key to the Genera of Sipunculoidea. 



I. The longitudinal musculature of the body-wall is continuous and not divided into 

 separate bands. The retractors of the introvert vary in number from one to four. 



1. Phascolosoma. — Two nephridia. Numerous tentacles surrounding the mouth in a circlet. A 



complete intestinal coil, unattached posteriorly (only in .1/. Hanseni attached) ; a spindle muscle 

 is usually present ; only on the anterior intestinal convolutions are there one or more ligaments. 

 Adhesive papillae are always absent. Hooklets arc generally not present on the introvert. The 

 retractors are four, two or only one. Eggs spherical. In all seas. 



2. Dendrostoma. — Two freely suspended nephridia. Only four to six pinnate tentacles. A complete, 



posteriorly unattached, intestinal coil ; spindle-muscle always present; ligaments present only on 

 the anterior intestinal coils. Hooklets are present, but may be shed early in life. Four or two 

 retractors. The contractile sac (of the vascular system) generally has caeca upon it. Tropical 

 forms. 



3. Phascolion. — A single ncphridium, only that of the right side, -which is attached to the body-wall 



throughout its length. The intestine forms no spiral or only an incomplete one ; there is no spindle- 

 muscle, whilst the loose intestinal loops are attached throughout their length to the body-wall by 

 numerous ligaments. Adhesive papilla; arc often present. The retractors are not more than two. 

 Eggs spherical. Living in Gastropod shells or in tubes. In all seas. 



II. The longitudinal musculature of the body-wall is divided into 17-41 separate bands. 

 Four retractores introversi. 



1. 1'hvmosoma. — Body covered with papillae. Numerous filamentous tentacles, which seldom (or 

 never ?) surround the oral aperture, but are arranged away from the latter, dorsally in a three- 

 quarter-circle which is open dorsal-wards. No caecurn on the rectum. Hooklets nearly always 

 present on the introvert. Four retractors (in P. Ruppellii two?). Contractile sacs almost always 

 devoid of villi. Eye-spots are always present. Eggs elliptic, flattened, reddish. Small tropical 

 species. 



5. Sipunculus. — Body without papillae. Tentacles surrounding the mouth in a circlet. Always one 



or several caeca on the rectum (except in »S. edulis ?). Hooklets absent, only present in S. australis. 

 Eggs spherical. The individual tentacles thick, with an internal vascular network (not three 

 longitudinal vessels merely) ; generally two contractile sacs. Mostly large forms. In all seas. 



III. In front of the anus and also at the hinder end of the body a distinct shield 

 {corneous thickening of the integument), or in front of the aims a calcareous ring or a 

 tube-like coruification, forming the base of the introvert, and another at the tail-end. 

 Hooklets sometimes present. Longitudinal muscles continuous or divided into bands. 



6. Aspidosiphon.* — An anal and a caudal shield. Introvert eccentric arising from beneath the anal 



shield ventrally. Tentacles small and not numerous, placed in a semicircle above the mouth. 



* See Dr. C. Ph. Sluiter, " Beitriige zu der Kennfcniss der Gephyreen aus dem Slulayischen Archipcl.,'" Natuurk. 

 Tidsch. v. Nederlandsch-Indie, Deel xliii. (1884), pp. 20-88, with 4 plates. 



