218 THE AMERICAN MONTHLY [September, 



In Zygosteplianiis and Semajitis there are 2 rings. The 

 former has 2 rings complete, perpendicular to one another, the 

 latter a vertical ring bearing on its base a horizontal ring. 



And in Acant/iodcs?)iia there are 3 rings, 2 incomplete mer- 

 idional rings, both truncated by a complete horizontal basal 

 ring. 



In the next 26 genera the skeleton is 



Cone-Shaped and has but One Chamber. 



If the shell is not Jointed it is either Halicalyptra or Co7-nn- 

 tella. The mouth of the former is surrounded by feet; the shell 

 of the latter is composed of lattice-work and dilates towards the 

 mouth. 



If the shell is 2-jointcd it is one of the next twelve genera in 

 the order given above. 



Lophophcetia and Dictyocephalus have no radial appendages, 

 and the latter has no horn, while the former has 2 or more. 



DictyopJiijnus^ Lych^iocaniun ^ I^itJiomelissa., and Lltlwpcra 

 have 3 radial appendages. If the mouth of the thorax is closed 

 it is the last. Here we have an exception to the general rule of 

 the second group, namely, the presence of one large mouth or 

 opening. The general shape of the form, however, will enable 

 the student to locate it in this group. 



Lychnoca7ii7im has 3 feet on the tnont/i^ Dictyophimus 3 ribs 

 on the thorax also, while in Lithomelissa the 3 ribs on the thorax 

 are prolonged into wings. 



The remaining 6 genera have numerous radial appendages. 

 Sethamphora has smooth radial ribs enclosed in the wall of the 

 thorax. The rest have no ribs in the thorax and Carpocaniiim 

 has no horn and the cephalis or ist joint is but slightly developed, 

 while in Aiithocyrtonia and allies the cephalis is well developed 

 and has a horn at the top. 



Anthocyrtoma has 6 feet around the mouth, Anthocyrtis 9, 

 Atithocyrtiuni 12 or more. Feet outside the restricted mouth 

 distinguish Afithocyrtiditcm . 



If the shell is J-Jointed it belongs to the next 10 genera of the 

 preceding list. And from 4 to 9 radial appendages will make it 

 either Cycladophora or Calocyclos., the mark of the latter being 

 the presence of feet around the mouth. The rest have only 3 

 radial appendages. Here again we are helped by an additional 

 fact. If the mouth is closed it is Lithornithiiim., Rhopalocaniitni 

 or Lithochytris. The first has 3 wings on the tkora.\\ the second 

 3 wings on the abdomen., the third has 3 terminal feet and is pyr- 

 amidal. But if the mouth is open it is one of the other five. Ptero- 

 canium has 3 ribs prolonged into 3 terminal feet, Pterocodon 3 

 free wings on the thorax and numerous terminal feet. Podocyrtis^ 

 Thyrsocyrtis and Dictyopodiutn have free appendages only on 

 the abdomen. In the first the feet are solid and simple, in the 

 second solid and ramified, in the third latticed. 



