48 N. Annandale : The Fauna of Brackish Ponds. [VOL. I, 



of the mesenteries often of a deep purple ^ which may be visible exter- 

 nally ; tentacles semi-opaque, often with irregular transverse bars of 

 opaque white. Column cylindrical, as broad or almost as broad as 

 high when normally expanded, broader than high when contracted ; 

 in the latter condition mound-shaped, with a considerable oval 

 aperture as a rule remaining open above the tentacles. Tentacles 

 elongated, tapering, perforate at the distal extremity, arranged in 

 five cycles ; the innermost cycle with six tentacles, the next with 

 twelve the third with twenty-four, the fourth with forty-eight, the 

 fifth with ninety-six : i86 in all (approximately). Disk ample, oval, 

 not separated from the column when expanded ; the mouth large, 

 elongated and narrow ; the lips protuberant, with six folds on either 

 side of the mouth ; the stomodseum extending more than half way 

 down the column ; the gonadial grooves distinct. External surface 

 of the column smooth, generally with rows of suckets arranged ver- 

 tically; the cinclides, which are difficult to detect in preserved speci- 

 mens, scattered. Basal disk variable in outline, often extending be- 

 yond the periphery of the column, provided with a distinct sphinc- 

 ter, which is visible in living specimens as a thin, semi-opaque ring 

 Circular muscles of the column well developed, confined to the 

 mesoderm ; the sphincter elongate in vertical section, consisting of 

 comparatively feeble folds without muscle spaces ; radial muscles 

 of the disk and tentacles situated at the base of the ectoderm 

 and not encroaching on the mesoderm. The six primary (complete) 

 pairs of mesenteries fertile ; sometimes the first and rarely also the 

 second secondary cycles fertile ; the number of secondary cycles 

 from three to five, each consisting of twelve mesenteries ; some 

 mesenteries in one or more of the cycles rudimentary, without fully 

 developed retractor muscles and devoid of filaments ; acontia very 

 long. Gonads protogynous, the two elements being produced at 

 different times and in different parts of the mesenteries, the ovaries 

 above the testes. 



Description of an Isolated Race (var. exul) of the Species. 



Column several times as long as broad, vermiform when extended 

 in young specimens sausage or barrel-shaped when contracted. 

 The walls of the column very thin, allowing forty-eight mesenteries 

 to be visible externally as narrow, semi-opaque vertical stripes. 

 Tentacles as in the typical form, except that there are never more 

 than four cycles ; the disk in old specimens much reduced, 

 divided into twelve distinct parts. The stomodseum extending 

 less than half way down the column. Basal disk devoid of a 

 sphincter, its periphery merging gradually into the column. The 

 folds of the subtentacular sphincter markedl}' deeper above than 

 below, with a few oval muscle spaces above. The six pairs of 

 primary mesenteries alone fully developed, the others as a rule lack- 

 ing retractor muscles and filaments, but the first c^^cle, or some of 

 its members, sometimes being fertile though feebly muscular. 

 Cinclides in vertical rows on the upper part of the column. 



