1892.] MICROSCOPICAL JOURNAL. 217 



lya^ Hymcniastrzim, or one of its two allies. If there are no 

 spines or chambered arms it is either the first or second, and an 

 equatorial girdle will make it PericJilamydium. Stylodictya 

 has 5 or more spines. Hyfueniastrum ^ Histiastrutn and Stcph- 

 attastrum have radial chambered ar?ns with or without solid 

 spines at the ends ; the first has 3 arms, the second and third 4. 

 Step/ianasir?/tn may be known by the presence of a terminal 

 girdle. 



The student will note that some of these genera are very much 

 alike. Ilymcnactura and Hymeniastr7an both have 3 radial 

 chambered arms and connecting membrane or network between 

 the arms, Statu-actura and Histiastru7n both have 4 such arms 

 and connecting membrane. So that it is hard to distinguish 

 these genera respectively. The point to note especially is whether 

 the surface is convex, /. e., lens-shaped, or comparatively flat. 

 If the former, it is Hymenactjira or Staiiractura^ as the case 

 may be ; if the latter, Hyvieniastrnm or Histiastrum. The 

 presence of the porous sieve plate is also another mark b}' which to 

 recognize Hymeniastrum aad Histiastrum. 



Passing now to the second grtmp, which is as a rule character- 

 ized by the presence of one large mouth or opening instead of 

 many small ones, we have these 36 genera to consider : 

 Lithocircus., Dictyocephalus, 



Zygocircus^ Pterocanitim, 



Zyg-ostepkanus, Pterocodon., 



A canthodesmia , Podocyrtis^ 



Semantis= Stcphanolithis. Thyrsocyrtis^ 



Malicalyptra , Dictyopodium , 



Cortiutella , Lithornithium , 



DictyopJiimus., Rhopalocanitiin ., 



L ithomelissa , L ithoch ytris^ 



Lychftocanizim., Cycladophora^ 



LitJiopera., Calocyclas^i 



Setkafup/iora {= Cryptop?-ora ^.), Eucyrtidium^ 

 Anthocyrtn7na^ Lithocampe., 



Anthocyrtis., Petalospyris, 



Aft t ho cyrtiu ni , Cera tospyris , 



Anthocyrtidiwni^ Cladospyris^ 



Carpocanium, Pithobotrys., 



Pophophcena , Botryocyrtis^ 



A formidable array certainly but not so hard to master as 

 would appear at first sight, since they admit of several subdivi- 

 sions very plainly marked. Thus in the first five of the above 

 genera the skeleton is 



A Ring or Combination of Rings. 



In Pithocirciis and Zygocirc?is there is but a single ring and 

 branched spines distinguish the former. 



