574 PEOF. w. A. heedman's eeyised 



MiCEOCOSMUS, Seller, 1877. 



Body attached, sessile, not incrusted with a continuous 

 coating of sand. Apertures both 4-lobed. A fold of the mantle, 

 covered by the invaginated test, usually present at the base of 

 the siphons. 



Test coriaceous, thin but tough. 



Branchial sac with more than 4 folds upon each side. 



Dorsal lamina a plain untoothed membrane. 



Tentacles compound. 



Intestine forming a narrow loop, on the left side of the body. 



Gonads on both sides, on the left partly covering the 

 intestine. 



The species of Microcosmus may be distinguished as follows : — 



( Branchial sac with 5 folds on each side. 



j _ M. oligophyllus, Heller. (S. Atl.) 



[ Branchial sac with more than 5 folds on each side 1 



-. [Branchial sac with 6 folds on eaoh side 2 



\ Branchial sac with more than 6 folds on each side 3 



2 J Tentacles fewer than 12 J/. ^^e6a, Traust. (Pac.) 



" \ Tentacles 20, or more 4 



(Tentacles 20 ; doi-sal tubercle simple, cordate. 

 M. Helleri, Herdm. (Austr.) 

 Tentacles 28; dorsal tubercle complex, formed of 2 spiral cones. 

 M. Herdmani, v. l)r. (S. Atl.) 



g f Branchial sac with 7 folds on each side 5 



( Branchial sac with more than 7 ibids on each side 6 



With not more than 6 or 7 stigmata in a mesh 7 



With about 12 stigmata in a mesh... M. propinquus, Herdm. (Austr.) 



m /With 4-5 stigmata in a mesh 8 



\ With 6-7 stigmata in a mesh M.anchi/lodeirus,TreiUst. (W.Ind.) 



g r Surface of test rough, corrugations irregular and granular 9 



[Surface n()t so rough, corrugations regular and smooth 10 



I With an extraordinarily long branchial siphon. 

 9 j _ M. scrotum, D. Ch. (Med.-) 



[Branchial siphon not very long M.polymoriphus,'S.el\ev. (Med. & 



[Austr.) 



f Pinnae of the tentacles unbranched, 12-14 bars on branchial fold. 

 M. vulgaris, Heller. (Atl. & Med.) 

 Pinnse of the tentacles bearing small pinnules, 18-20 bars on fold. 

 M. Sabatieri, Roule. (Med.) 



g [ Branchial sac with 8 folds on each side 11 



[Branchial sac with more than 8 folds on each side 12 



r With 16-20 tentacles, surface rough. M. exasperatus. Heller. (W. Ind.) 

 11 -^ With 20-25 tentacles, surface nearly smooth. 



[ M.distans,'Kel\&T. (W.Ind.) 



j2 I Branchial sac with 9-10 folds on each side 13 



[Branchial sac with 12 or more folds on each side 14 



fThe 3 lower folds do not reach oesophageal aperture. [W. Ind.) 

 ^^ "> M. variegatus. Heller. (Med., 

 1 All the folds extending beyond the oesophageal aperture 15 



