REPORT ON THE DEEP-SEA MEDUSAE. 



xliii 



(" peronium ") keeps up the connection between the ectodermal epithelium of the 

 tentacle and the umbrella margin. The peronia transect the gelatinous body as far as the 

 subumbrella, and at the same time form deeper or shallower indentations at the dorsal 

 bases, which in the Peganthida3 (Pis. X.-XII.) become deep incisions of the umbrella 

 margin. The velum which fills them naturally appears much broader here than at the 

 margin of the underlying collar lobes ; it connects the latter in the same way as the 

 velarium of the Cubomedusae does the true marginal lobes of this order (§ 70). 



§ 69. Umbrella margin of the Acraspedse: lobe corona (" corona lobaris"). Whilst the 

 velum appears in all Craspedotas or Hydromedusse as a characteristic process of the umbrella 

 margin, it is generally wanting in all Acraspedse or Scyphomedusae. A velum-like mem- 



fig. D. Pcrkolpa quadrigata (Peromedusre, Pericolpidae). 



Subumbral aspect, (oi) Sense clubs (interradial). (oa) Ampulla at their bases, (t) Tentacles (perradial). 

 Ifil) Marginal lobes (adradial). (bu) Horseshoe-shaped canals of the lobes. (Jet) Peronia between 

 the two limbs of the canals, (s) Genitalia, (ml:) Root muscles of the tentacles. (md l ) Perradial 

 deltoid muscles, (md-) Interradial deltoid muscles, (ak) Oral ribs, (ar) Oral grooves on their 

 inner surface, (ai) Oral tseniola. (ti) Tentacle roots, (be) Coronal pouches, (mc) Coronal muscles. 



brane (" velarium"), which in some families of the latter (Charybdeidae, Aurelidse) forms 

 a narrower or broader membranous selvage at the umbrella margin (PI. XXVI. va), is 

 perfectly different from the true velum both as to origin and structure. On the other 

 hand, all Acraspecke have a lobe corona (" corona lobarum "). This is usually wanting in 

 the Craspedotse, as the gelatinoiis " collar lobes " which are developed in some groups of 

 the latter (Narcomedusge, Pis. IX.-XIV.), but are connected by the velum, cannot 

 be compared to the true marginal lobes of the Acraspedse. The latter may rather be 

 essentially considered as shallow, leaf-shaped " steering tentacles." They have one or 

 two longitudinal muscles on their concave subumbral surface, by whose contraction they 



