634 MEDUS/E OF THE WORLD. 



Maas, 1903 (Syphomedusen der Siboga Expedition, p. 89), proposes another system 

 based upon the character of the muscle-system of the subumbrella, the presence or absence 

 of ocelli on the sense-clubs, the character of the canal-system and of the mouth-arms. Maas's 

 system is as follows: 



Arcadomyaria: The subumbrella muscles are arranged in feather-like arcs. Mouth-arms elongate and irregularly pinnate 

 in their branching. Rhopalia with ocellus and without an exumbrella sensory pit. Radial-canals twice as numerous 

 as the rhopalia and connected by an anastomosing network of vessels. One or more ring-canals may or may not be 

 present. 4 separate genital sacs, with small, round, interradial ostia. There is only one family, the Cassiopeida. 



Radiotnyaria: Radial-muscles of the subumbrella better developed than the circular muscles. Mouth-arms bifurcated. 

 Rhopalia without ocelli and without exumbrella, sensory pits. 8 principal and other secondary radial-canals, all 

 connected by a marginal network. No definite ring-canal. Funnel-shaped genital ostia. A unitary subgenital 

 cavity may or may not be present. There is one family, the Cepheidt?. 



Cyclomyaria: Circular muscles of the subumbrella better developed than the radial-muscles, the latter being often absent. 

 Mouth-arms 3-winged, or derived from this type. There are 3 groups of the Cyclomyaria, as follows: 



(-4) 16 radial-canals which extend from the stomach to the bell-margin, and between them a blindly-ending, anastomosing 

 network of vessels. Mouth-arms with scapulcts. Genital ostia slit-like and divided by a median flap. Rhopalia 

 without ocelli, but with sensory pits with radiating furrows. Group A is equivalent to the Rhizostonitdtf+ Stomo- 

 lophidd: of Claus, or to the Rhizostomata scafiulata of Vanhbffen. 



(5) 8 rhopalar canals extend to the bell-margin and 8 in the inter-rhopalar radii end in the ring-canal. On its outer 

 side, the ring-canal gives off a network of anastomosing vessels, and on its inner side it gives rise to another network 

 which ends blindly without connecting with the stomach. 



(1) Mouth-arms j-winged, usually with pinnate lateral brandies. Genital ostia slit-like. Rhopalia with pigment 

 spots, and sensory pits with radiating furrows. This contains the family Lychnorhizidts of Claus; including 

 the genera Lychnorhiza, Crambione, and Crambessa. 



(2) Mouth-arms very elongate, triangular in cross-section. Genital ostia wide openings. Rhopalia with pigment 

 spots and furrowed sensory pits. This contains a part of Claus's family Leptobracht'dtf. 



(C) The 8 rhopalar extend to the bell-margin, and (8X) canals extend only to the ring-canal. On its outer side the 

 ring-canal gives off a narrow network and on its inner side is a network of wider mesh. 



(1) Mouth-arms very elongate, triangular, file-shaped. Genital ostia wide slits. Genera: Thysanostoma, Lepto- 

 brachia, and Himanostoma of Claus's Leptobrachidae. 



(2) Arms j-winged, not elongate. Ostia wide. Rhopalia with ocelli and small sensory pits without furrows. 



This is equivalent to Claus' family Catostylidcs containing the genera Loborhiza, Crossostoma, and Mastigias. 



The Arcadomyaria of Maas is only a new name for Vanhoffen's Rhizostomata pinnata, 

 the Radiomyaria are equivalent to Vanhoffen's Rhizostomata dichotoma, and the Cyclomyaria 

 includes rather confusedly the trtpt era -\-tngona-\- scapulata -\-lonf era of VanhofFen. Maas's 

 system is erroneous in some respects; for example the rhopalia of Casswpea xamachana have 

 pigment spots while those of Casswpca frontiosa have none; similarly Crambessa tagt has 

 ("ocelli") pigment spots but Crambessa mosaica has none. It is therefore evident that the 

 presence or absence of "ocelli" does not afford a suitable criterion for the separation even 

 of genera. The exumbrella sensory pits may have furrows, in one species of a genus and 

 be simple in another, as in Rhopilema esculent a and R. verillii. In my opinion the older and 

 simpler system of VanhofFen is to be preferred to this complex scheme proposed by Maas. 



In view of the observations of Schultze and of Maas, we may amend Vanhoffen's system 

 as follows: 



Rhizostomata pinnata; Rhizostomae with 8 separate, elongate, linear mouth-arms which give rise to pinnately or com- 

 plexly arranged side branches (figs. 4, 5, and 7, plate 69). The circular muscles of the subumbrella tend to be 

 bowed outward in a series of arcs on both sides of each radial-canal, the convexities alternating with the canals. The 

 genera are as follows: Torcutna HA ECKEL, 1880, with 8 rhopalia. 



Cassiopea PERON AND LESUEUR, 1809, with more than 8 rhopalia. 



Rhizostomata dtchotoma: 8 separate mouth-arms, the lower parts of each one of which is V-shaped in cross-section, the 

 apex of the V being centrad, and the rays directed outward (fig. 404, p. 650) The mouths are developed upon the 

 ventral sides of the mouth-arms. The radial-muscles are powerfully, and the ring-muscles weakly, developed. The 

 radial-canals are all connected by a marginal network of vessels, without a definite ring-canal. The genera are as 

 follows: 



Cephea PRON AND LESUEUR, 1809. Exumbrella with a central dome bearing solid, wart-shaped protuberances. 

 Cotylorkiza L. AGASSIZ, 1862. With a smooth, simple dome at the center of the exumbrella. 

 Polyrltiza L. AGASSIZ, 1862. Exumbrella with a central depression and with radiating furrows. 



Rhizostomata triptera: 8 separate mouth-arms the lower parts of each of which is Y-shaped in cross-section, due to the 

 development of 2. lateral, dorsal, and a median ventral, longitudinal lamella, all 3 of which taper to a point at the 

 lower end of the arm. The mouths are developed upon the free edges and partially over the sides of the 3 lamellae 

 or wings of the mouth-arms (fig. 41 1, p. 664) The ring-muscles are powerfully and the radial-muscles weakly, devel- 

 oped. A ring-canal with a network of anastomosing vessels arising from its inner and outer sides is usually present. 

 Mouth arms without scapulets. The genera are very closely related and are as follows: 



Catostylus L. AGASSIZ, 1862= Toxocl\tus+ Crambessa HAECKEL. Mouth-arms without filaments, clubs, or other 

 appendages. The network of vessels arising from the inner side of the ring-canal ends blindly, without con- 

 necting with the stomach. 



Lychnorhiza HAF.CKEL, 1880. With filaments but without clubs upon the mouth-arms. In other respects similar 

 to Crambessa. 



