CONSPECTUS OF THE FAMILIES AND Cl M.K'A. 27 



Spines (setae!) marginal; on both valves; valves 



dissimilar, mostly hyaline HERCOTHECA LXI. 



All others, valves frequently awued ; or with minute 

 5. { scattered spines ; or dissimilar ; hvaliue, or im- 



I * 



perfectly silicious ; or frustules compound; awns 

 often absent in fossil forms; leaving- valves ni- 



tirely smooth CH.*;TOCEROS LXII. 



FAMILY X. MELOSIEE.^. 

 r Frustules apiculate ( drawn out at the extremities or 



margins to a point) 1 



I Frustules not as above 2 



f Frustules cylindrical ; apiculate in f. v. ; valves 



j, I unlike.. PYXILLA LXIII. 



j Frustules not cylindrical ; apiculate in s. v. ; valves 



alike Peponia LXIV. 



f Valves with a central spine, or coronal or scattered 

 2 spines ; not ribbed ; frustules cohering by the 



i spines STEPHANOPYXIS LXY. 



I- Valves and frustules not as above 3 



f Frustules cylindrical ; with somewhat large regular 

 j marginal teeth, and peculiar central clasping spine. 



Syndetocystis LX v i . 



t Frustules not as above 4 



f Valves elliptical or constricted; with marginal spines 

 . or teeth; and central, peculiar nodule 



EUTILARIA LXYII. 



I- Valves not as above 5 



f Frustules cylindrical ; ends constricted and finally 



f. expanded into a connecting nodule 



8trangulonema LXVIIF. 



L Frustules not as above <> 



f Frustules cylindrical ; with a border of much elori- 



Q gated cells at junction of margins in f. v 



j Skeletonenia LXIX. 



I Frustules not as above 7 



r Valves circular ; with curved marginal rays, and 



7. -j minute marginal teeth DISCOSIRA=MELOSSRA LXXII 



(. Valves not as above 



Valves dissimilar ; somewhat conical or inflated in 

 f, v. ; with radiating lines or ribs ; not branching, 

 nor bifurcate at extremities ; apex truncated ; 

 j usually spinous ; interspaces punctate.. 



STEPH ANOCOMA i,\ \. 



I Frustules not as above ' 



