374 MEDTJSjE OP THE WORLD. 



separated one from another by the mesenterial partitions which form groined arches uniting 

 the 8 stomach-rays to the subumbrella and extending outward to bell-margin. We may 

 therefore speak of the gonads as 8 double, genital organs divided by 8 median partitions into 

 16 separated gonads. Maas regards the 8 stomach-pouches as the basal parts of the radial- 

 canals, and if this view be true the gonads may be considered as being on the sides of the gastric 

 regions of the radial-canals. The development of this medusa is, however, entirely unknown, 

 and this point can only be determined through studies of the ontogeny. 



This is an Arctic species. Haeckel records it from a depth of 1,250 fathoms off Nova 

 Scotia and off the west coast of Greenland. Gronberg found it off the coast of Spitzbergen, 

 where it occurs within 10 to 30 fathoms of the surface. Browne records it from the Arctic 

 coast of Norway, between depths of 250 fathoms and the surface. Levinsen, 1893, Maas, 

 1893, and Aurivillius, 1899, record it from the coasts of Greenland. Linko, 1900, 1904, 

 found it off the Murman coast, northern Russia, and Maas, 1906, near King Charles Land 

 from depths between 25 to 75 fathoms. It appears to be common along Arctic coasts. 



Browne, 1903, gives the best modern account of this medusa and has corrected several 

 serious errors in Haeckel's, 1881, description. 



Broch records this medusa from a depth of less than 43 fathoms at Winterhafn, and it is 

 evident that this species can not be called a "deep-sea medusa." 



Ptychogastria asteroides Browne Maas. 



Pectanthis asteroides, Haeckel, 1879, Syst. der Medusen, p. 267; 1881, Report Challenger Expedition, Zool., vol. 4> p. 20, 



plates 7, 8; figs. 1-10. 

 (Pt\chogastria f) asteroides, Browne, 1903, Bergens Museums Aarbog, No. 4, p. 29. 

 Ptychogastria asteroides, Maas, 1906, Fauna Arctica, Bd. 4, Lfg. 3, p. 492, Jena. 



Bell about 4 to 5 mm. wide, flatter than a hemisphere, with fairly thin, gelatinous walls 

 and a small, solid, sharply pointed, apical projection. 16 raised, radiating ridges extend from 

 center of exumbrella to margin; of these, 4 are radial, 4 interradial, and 8 adradial. The 8 

 radial and interradial ridges are each marked by a streak of purple-red, which expands into a 

 large spot at the margin. All 16 ridges bear nematocysts. The margin exhibits 16 rounded 

 lobes, alternating with the 16 ridges of the exumbrella. This margin is thickened by a consid- 

 erable development of nematocysts, the inner border of which is black, ciliated, and sinuous, 

 with about 8 to 10 short sinuosities in each lappet. There are 16 isolated, short, bluntly 

 conical tentacles, one in each of the 16 niches between the marginal lobes and in the radii of 

 the 16 exumbrella ridges. At the center of the margin of each lobe, alternating with the 

 exumbrella ridges, is a single lithocyst. These 16 lithocysts are short and club-shaped and 

 each contains a terminal spherical concretion of entodermal origin. 



There are 200 to 260 tentacles, which arise in 16 clusters from the 16 marginal lobes on 

 both sides of the 1 6 lithocysts. These tentacles are hollow, flexible, and usually somewhat 

 shorter than the radius of the bell, although they are capable of great extension. Nearly all of 

 the tentacles are provided with a terminal sucker, and their general appearance is strongly 

 suggestive of the ambulacral tube-feet of echinoderms. The medusae may attach themselves 

 by means of the terminal suckers of their tentacles and may then climb upward as would a 

 star-fish. Frequently the medusa lies upon the bottom with its exumbrella downward and 

 is then anchored by some of its suctorial tentacles while others wave freely about in the water. 

 A few of the tentacles have simple, pointed ends without terminal suckers. 



Velum thick and provided with powerful circular muscles. It can be contracted so as to 

 close the opening of the bell-cavity, like a sphincter. The central stomach is 4-sided and 

 gives rise to 8 straight, slender radial-canals, 4 radial and 4 interradial. These 8 canals extend 

 to the marginal ring-canal in the radii of 8 alternate notches between alternate lappets of the 

 bell-margin. 



The 8 radial-canals are bound to the sides of the stomach by 8 well-developed septa, 

 forming 8 shelf-like, radiating partitions on wall of subumbrella. The 8 egg-shaped gonads 

 are developed upon the proximal thirds of the 8 radial-canals closely adjacent to the wall of the 

 stomach. Each of these 8 gonads is bound across its middle axial line by the mesenterial 

 septum which extends from along the radial-canal to the stomach-wall. Each gonad contains 

 a single, central lumen connected with the radial-canal. The stomach is a simple, narrow, 



