400 PERCY SLADEN TRUST EXPEDITION 



and obliquely placed. The ectodermic longitudinal muscles are well developed, but there 

 are no ridges of the structureless lamella for their support. 



The mesenterial filaments have numerous granular glands and some large deeply 

 stained nematocysts vs^ith a light central axis. The stomodgeum has well developed ridges, 

 and its ectoderm has both the tentacular and mesenterial nematocysts as well as granular 

 gland cells. 



The endoderm is much vacuolated. It forms a definite layer on the walls of the 

 stomodaeum and of the column, but most of this region is filled in with delicate tissue, no 

 definite boundary limiting the mesenteries. Near the aboral end the mesenteries are well- 

 defined and leaf-like in section. 



Log. Providence reef, off Cerf Island, surface. 



Genus OvACTis, v. Beneden. 



V. Beneden defined the genus as follows* : " Larves ovo'ides ou pyriformes, qui Ton 

 prendrait a, premiere vue pour des oeufs. EUes portent a la peripheric du disque buccal un 

 cercle de mamelons tentaculaires marginaux, si peu saillants, qu'a peine ils s'aperjoivent a 

 I'oeil nu, quoique les larves mesurent plusieurs millimetres suivant leur grand axe. L'ap- 

 parition du tentacule median est tres-tardive ; elle est toujours posterieure a la formation 

 des quatre premier couples de tentacules marginaux. II n'en existe encore aucurie trace 

 chez des larves pourvues de douze tentacules chez 0. hrasiliensis. On peut en dire autant 

 des tentacules labiaux. Je n'ai trouvd aucune indication de ces organes chez aucune des 

 especes rapportees h. ce genre. Le c6ne buccal est peu saillant. II existe des fibrilles 

 musculaires longitudinales sur les deux faces des sarcoseptes lateraux. Les cloisons S^ 

 seules portent des aconties. Les cloisons directrices atteignent k peu pres le p61e aboral." 



The two larvae in the collection are neither egg-shaped nor pyriform, but sub-spherical, 

 flattened on both their oral and aboral surfaces. No longitudinal muscular fibres are found, 

 on the lateral mesenteries and there are no acontia. The time of the development of the 

 median tentacle is not known, but in the second larva (larva III.), where there are tenta- 

 cular processes, the median process is the smallest so that it is evidently late in developing. 



6. Larva II. Ovactis superjicialis, n. sp. (PI. 24, fig. 14.) 



The larva is colourless, translucent and almost spherical, flattened orally and con- 

 siderably depressed aborally ; its length is 2 mm. and its maximum diameter 2 '8 mm. On 

 each side of the median plane the oral surface is raised forming the lips of the buccal cone. 

 There are no tentacles nor rudiments of tentacles. 



In transverse section the stomodseum is small, quadrilateral above, but nearer the 

 enterostome broadly elliptical. A sulcar groove is difierentiated, there are storaodeeal 

 ridges near the enterostome, and both hyposulcus and hemisulci are present but short. 

 There are 17 mesenteries which are all complete, 8 on the right and 7 on the left of the 

 2 directives. Mesentery 8 is the shortest, then mesentery 7 I and next mesentery 7 r. 

 With the exception of mesentery 6 I, which nearly reaches the base, all the mesenteries 

 extend to the aboral end. The mesenteries in transverse section are somewhat leaf-like in 



* loc. cit. p. 84. 



