[29] 



MEDUSA FROM THE GULF STREAM. 



955 



examination of the velarium, shows me the error of such a view as far 

 as the systematic determination of the species goes. It was s-een that 

 in almost all cases the velum is broken up into ])arts resembling- mar- 

 ginal lapi)ets, breaking along the lines of the peronite, thus giving us 

 structures which closely resemble the marginal lobes of the Acraspeda. 

 Several of the peroniie are still unbroken in certain specimens, enabling 

 me to observe the anatomy of this region of the disk margin. Although 

 the majority of the specimens have the velarium broken into marginal 

 lappets, the union of these marginal lappets in several instances was 

 thought to prove that the lappets are nominally united in all specimens. 



The umbrella is discoid in shape, slightly convex above, flexible in 

 alcohol. The velarium {vel.) hangs from the lower outer rim of the disk, 

 and is crossed by a number of vertical ribs (fig. 2, per.) connecting with 

 the free edges of the velarium and the tentacular bases. These bodies 

 (peronioe) are always the lines along which a break occurs when the 

 velarium is divided into the bodies which resemble and are supposed to 

 be homologous with the marginal lappets {)ng. li).). 



The exumbrella has from 24 to 32 shallow radial depressions {fos. rad.) 

 or furrows, found near the periphery. These furrows are separated from 

 each other by the same number of radial, generally more or less polyg- 

 onal, elevations {col. sub.), which lie in the same radii as the tentacles 

 and peronise. There are consequently the same number of tentacles as 

 of peroniae. 



Spechnens examined. 



The umbrella is flat, discoid, rounded-convex at edges. The vertical 

 thickness of the bell walls at the center of the disk is much less than in 

 the zone of the radial subumbral elevations. Horizontal diameter 

 SO-lOO"^™. On the subumbral side of the disk there is a zone of radial 

 furrows {fos. rad.), which begins a short distance from the union of the 

 velarium (re/.) with the periphery of the umbrella and extends ceutrip- 

 etally 10-15™"' from the same. These incisions are shallow trenches in 

 the subumbral side of the umbrella between elevations {col. sub.) which 

 lie in that zone. The number of these elevations is equal to that of the 

 tentacles. 



Within the disk in a single specimen there is a cavity (f/a.) formed by 

 a splitting of the gelatinous walls, the rim of which is seen through the 

 wall of the subumbrella, and extends nearly to the internal margin of 

 the zone of radial elevations. This cavity is probably entered by a cen- 



