522 MEDUSA OF THE WORLD. 



view that the Stauromedusae are degenerate, and, indeed, degeneracy would very probably 

 result from their sessile condition. 



The Tesseranthinae, known only through the works of Haeckel, who alone has observed 

 them, appear to be pelagic and are said to differ from other Stauromedusae in having solid, 

 tapering, non-knobbed tentacles, and in lacking marginal lobes. Their relationship to the 

 Stauromedusae is uncertain. Only 4 specimens have ever been taken and these are described 

 by Haeckel from preserved material. It will be well to suspend judgment in respect to their 

 structure, relationship, and development until more specimens have been studied. 



The sessile Stauromedusae are creatures of cold seas. None is known from the tropics. 

 They are littoral forms and attach themselves to Fucus, Zostera, and other seaweeds among 

 the tidal eddies of the coast. They are generally rare and only locally abundant in any case. 



Owing to their rarity many of the species of Stauromedusae are imperfectly described, 

 and it is probable that some of them should be reduced. Kassianow, 1901, has studied the 

 nervous system of Liicernana, Haliclystus, and Craterlophus, and the results of his studies 

 are here reviewed in the discussion of the genus Lucernaria, wherein I have also reviewed 

 the brief observations of Fol and of Kowalevsky, 1884, upon the early stages of the develop- 

 ment of Lucernaria. 



The sessile Stauromedusae display no rhythmical pulsation in their bells, but no studies 

 have been made to discover whether the larvae at any stage possess this power. Hornell, 

 1893, and Browne, 1896, have studied the variations of Haliclystus octoradiatus. The results 

 of their studies are referred to in the description of this species. 



According to A. Meyer, 1865, the Lucernaridae have great regenerative power. The bell 

 may reproduce a new stalk and parts of the medusa may regenerate the whole (see genus 

 Haliclystus}. Kassianow, 1901 (Zeit. fur wissen. Zool., Bd. 69, p. 371), reports upon some- 

 what similar experiments upon Craterlophus. 



The relationship which may exist between the Stauromedusae and the Carybdeidae is 

 discussed in the introduction to this volume. 



Genera TESSERA, TESSERANTHA, and TESSERARIA Haeckel, 1880. 



Tessera, Tesserantha, HAECKEL, 1880, Syst. der Medusen, pp. 373-375; 1 88 1, Deep-Sea Medusae Challenger Exped., vol. 4, p. 49. 

 Tesseraria, HAECKEL, iSSo, Syst. der Medusen, p. 633. 



Haeckel describes 4 specimens of these medusae from preserved material, and is the only 

 naturalist who has seen them. They are said to differ from other Stauromedusae in their solid, 

 non-knobbed tentacles, and in their being free-swimming, non-attached forms. 



Haeckel states that these medusae have a simple, uncleft, umbrella margin, no marginal 

 anchors, but 8 to 16 simple, perradial, interradial, and adradial tentacles. The broad marginal 

 ring-muscle of the subumbrella is entire, not divided into 8 isolated sectors. Centripetal to 

 the ring-muscle there is a system of radial-muscles. The medusae are pelagic and have no 

 stalk of attachment, although a hollow apical projection is found at the aboral pole of the bell. 

 The tentacles are solid and do not terminate in nematocyst-knobs. 



The stomach gives rise to 4 wide, perradial, gastric pouches which are possibly divided 

 one from another in the 4 interradii by 4 short, narrow septa. These septa extend centniugally 

 from the 4 gonads, but are so short that they do not reach the bell-margin, and thus there is a 

 wide, marginal, gastral ring-sinus. There are 4 interradial, horse-shoe-shaped gonads with 

 their free ends pointing outward. 4 simple lips and 4 interradial areas of gastric filaments in 

 the stomach. 



According to Haeckel these 3 genera are distinguished as follows: 



Tessera, with 8 tentacles, 4 perradial and 4 interradial. Bell 4 to 8 mm. wide. 



Tesseranlha, with 16 tentacles, 4 perradial, and 4 interradial, and 8 adradial. Bell 6 mm. wide. 



Tesseraria, with 32 tentacles. Bell 10 mm. wide. 



In all respects these medusae resemble one another so closely that I am lead to suspect 

 that they may prove to be but stages in the growth of one and the same medusa. It will be 

 observed that the larger medusae have the greater number of tentacles. 



The following is a brief diagnosis of the characters of these medusae, according to Haeckel: 



Tessera princeps Haeckel, 1880 (Syst. der Medusen, p. 347, taf. 21, fign. 1-6), is 5 mm. 



high and 4 mm. wide, with a pyriform bell and hollow apex. There are 4 perradial tentacles 



about as long as the bell height, and 4 shorter (undeveloped ?) interradial tentacles. There 



