COHONAT^ — ATORELLA. 569 



lappets. The stomach is flat and shallow and the 4 lips are short and thickened. The 4 

 interradial septal nodes are narrow and the perradial ostia wide. The gastric cirri are 

 arranged in 4 interradial groups, each group arising from a stout gelatinous stalk, and consist- 

 ing of 80 to 100 filaments. The canal-system of the bell resembles that oi Periphylla. The 4 

 perradial ostia of the central stomach lead into a wide ring-sinus, which gives rise on its outer 

 side to 12 broad radial-canals in the radii of the tentacles and sense-organs. These radial- 

 canals branch at their ends and unite to form a marginal festoon canal. The ring-muscle of 

 the subumbrella is very weak, but the subumbrella plates at the bases of the tentacles are 

 very prominent. 



There are 4 gonads, each being a leaf-shaped body folded so as to leave a deep groove 

 along us middle line on the inner surface, and this groove causes the gonad to appear as if 

 double, although this is not truly the case for each gonad is attached along a single line. The 

 gonads are orange-yellow, all other parts colorless. This is a surface species. Bigelow records 

 it from off the Pacific coast of Panama. 



Order SEMAEOSTOME.S L. Agassiz, 1862, 



SeniaeoUotne^r, .Agassiz, L., 1862, Cont. Nat. Hibt. U. S., vol. 4, pp. 9, 159. 



Semoitonue, Haeckel, 1880, Syst. der Mcdusen, p. 499. 



Settiteoitoniata, Vanhoffen, 1888, Bibliotheca Zoologica, Heft. 3, pp. 6, 21; 1906, Nordisches Plankton, Nr. 1 1, Acraspedas, p. 45. 



SeniaeostoirttSy Maas, 1907, Ergeb. und Fortschritte der Zool., Bd. I, p. 200; 1906, Fauna .Arctica, Bd. 4, Lfg. 3, p. 504. 



Discomedusce (in part), Haeckel, 1880, Syst. der Medusen, p. 450. 



CHARACTERS OF THE SEMAEOSTOMEjE. 



Sc)phomedusae without a coronal furrow and without pedalia. With a simple, central 

 mouth-opening, the 4 perradial angles of which are developed into large curtain-like or gelat- 

 inous lips. With hollow tentacles and marginal rhopalia. The gonads are in sac-like folds of 

 the entodermal wall of the subumbrella. Without interradial septal nodes in the stomach. 



The families of the Semaeostomeae are as follows: 



(1) Pclagidee Gegenbaur, 1856. The central stomach gives rise to completely separated, unbranched radiating pouches. 

 No ring-canal. Tentacles arise from the bell-margin between the clefts of the lappets. 



(2) Cyaneida; Agassiz, L., 1862. The central stomach gives rise to branched but completely separated radial-canals. 

 No ring-canal. Tentacles arise from the floor of the subumbrella. 



(3) Ulmarida? Haeckel, 1880, sens ampl. The central stomach gives rise to simple or branched radial-canals which 

 are put into connection one with another by a marginal ring-canal. 



A. Subfamily Umbrosidii. The tentacles arise singly from the clefts between the marginal lappets at the bell- 



margin. Protrusive, sac-like gonads, without subgenital pits. 



B. Subfamily Sthenonidii. The tentacles arise in linear clusters from the floor of the subumbrella. 



C. Subfamily Aurelidii. The tentacles and lappets arise from the sides of the exumbrella above the margin. 



Invaginated gonads with subgenital pits. 



Family PELAGID.*; Gegenbaur, 1856. 



PelagiJx, Gegenbaur, 1856, Zeit. fiir wissen. Zool., Bd. 8, pp. 210, 267. — Agassiz, L., 1862, Cont. Nat. Hist. U. S., vol. 4, pp 

 121, 163.— Agassiz, A., 1865, North Amer. Acal., p. 47.— Haeckel, 18S0, Syst. der Medusen, p. 499.— von Lendenfeld, 

 1S84, Proc. Linnean Soc. New South Wales, vol. 9, p. 265.— Glaus, 18S6, .Arbeit. Zool. Inst. Univ. Wein., Bd. 7, p. no. — 

 Agassiz and Mayer, 1898, Bull. Mus. Comp. Zool. at Harvard College, vol. 32, p. i.— Claus, 1883, Organisation und 

 Entwick. Medusen, p. 24. — VANHorrEN, 1906, Nordisches Plankton, Nr. 11, p. 45. 



FAMILY CHARACTERS. 



Scyphomedusae with 8 or i6 marginal sense-organs, 4 perradial and 4 interradial, and, 

 when present, 8 adradial. 8 or more tentacles which arise singly from the clefts between the 

 marginal lappets. 16 to 64 marginal lappets. The mouth is simple and cruciform, and is 

 situated at the extremity of an oesophagal tube, the 4 perradial corners of which are produced 

 to form 4 long mouth-arms, the free edges of which are complexly crenulated. The simple, 

 lenticular, central stomach gives rise to completely separated, radiating pouches the centrifugal 

 ends of which give rise to simple, unbranched lappet-pouches. There is no ring-canal. The 

 gonads occupy 4 interradial folds in the wall of the subumbrella. In some cases they project, 

 but they are usually sunken, forming 4 pits in the floor of the subumbrella. 



