[9] MEDUSA FROM THE GULF STREAM. 935 



The most marked character which strikes the attention in looking at 

 the disk of Atolla from the aboral or exumbral side is a ring-shaped 

 furrow or ditch {fos. cor.), situated at about two-thirds the distance from 

 the center of the disk to its periphery. This ditch will be called, in our 

 subsequent descriptions, the coronal ditch or furrow {fos. cor.) ; the cen- 

 tral part of the disk, the discus centralis, or central disk {(lis. cent.), and 

 the peripheral portion the corona. The separation of the corona from 

 the central disk by the coronal furrow has suggested the generic name, 

 Atolla. 



A second marked feature, which a superficial study of the exumbrai 

 side of the umbrella partially shows, is a strong peripheral muscular 

 band {mvs. cor. e.) which, although belonging to the subumbral side of 

 the disk, is, in most of the specimens, by its contractions, brought into 

 view on the exumbral side, so that it appears as a light brown ring on 

 the margin of the subumbrella, shov/ing through between the intervals 

 of the gelatinous blocks which carry the marginal lappets. This mus- 

 cle {mus. cor. e.) reaches, in Atolla and Gollaspis, a most extraordinary 

 development. The umbrella of A tolla in alcohol is translucent and has 

 a bluish color, while the muscle, as may be said also in relation toother 

 muscles in the same medusa, has an opaque, light chestnut-brown color. 

 Between the coronal ditch and the peripheral muscle thus abnormally 

 brought to view on the exumbral side of the disk lie two rows of gela- 

 tinous blocks, confluent below the surface, yet superficially marked oft", 

 alternating with each other, which form the corona and bear either a 

 single tentacle or a small marginal sense-body with marginal lappets. 

 The short, solid (?) muscular tentacles {ta), in many alcoholic specimens 

 rise almost perpendicularly from the exumbral surface of the corona, 

 while the sense-bodies are borne on quadrangular or ijolygonal gelatin- 

 ous blocks {soc. s. b.), the bases of which are dovetailed into the inter- 

 stices on the peripheral side of those gelationus blocks {soc. ta), which 

 bear the tentacles. 



Seen from the subumbral side, the large peripheral coronal muscle 

 {mus. cor. e.) is found to have a greater width than when seen from the 

 exumbral. The most characteristic feature, however, of this region is 

 the stomach hanging from the subumbral walls of the middle of the 

 lower umbrella. This organ is a bag-shaped structure fastened on a 

 cross-shaped double line, with a simple mouth {or) opening at the free 

 end. The stomach opens by four orifices at the angles of the cross- 

 shaped body into an annular sinus included in the walls of the corona. 

 In the walls of the stomach are four broad, pouch -like plates {lb. per.) 

 alternating with as many narrow lobes {lb. int.), which are triangular- 

 shaped. The latter fuse with the lower walls of the umbrella and form 

 the re-entering angles of the cross-shaped attachments. On the inner 

 surface the " phacellen " are arranged in lines and are thickly matted 

 together in the stomach cavity, imparting a purple color to the inner 

 walls. 



