1891.] MICEOSCOPICAL JOURNAL. 101 



stalk. Podocystis is pear-shaped with a middle line. The valve of 

 Pyxidic7ila is circular and very convex. Tryblioiiella has a heavy 

 inner marginalline. Raphonels\\A'& ends produced. 



In the fourth, if the frustuleis wedge-shaped it is Licmophora^ Podos- 

 pJienia^ Rhipidophora or Clhnacosphenia. 



The frustules of the first form a fan ; the single frustule of the third, 

 with its long stalk, resembles a battledoor ; Climacosphenia has com- 

 partments ; Podosphenia has the ends indented, but no long stalk, and 

 the frustules are not united. If the heavy lines are not arched but straight 

 it is Striaiella,Phal)done?na^ or Gratnmatophora. Interrupted lines 

 will make itthe second, frustules in a zigzag chain the third. Anaulus 

 has indentations at the sides which show in either view. 



And in the last division CJicetoceros has valves with two long spines 

 or threads ; Rhizoselenia very long valves with conical ends tipped 

 with a spine ; Syndendrium ^%q\&\c\\ spines on one valve only : Syringi- 

 diuvi, valves unlike and two horns on one valve, one on the other. 

 The frustule of Isthmia is a rhomboid or trapezoid ; that of Biddulphia 

 and Amphitetras is quadrilateral, but the latter is flat, the former in- 

 flated. If the valve is triangular it is Priceratmm^ but Pricerathun 

 is sometimes quadrangular or even pentagonal. It is therefore hard at 

 times to distinguish Triccratium from AinpJiitetras. The angles of 

 Priceratium often have short horns or little teeth which may serve as a 

 guide, and the frustules of Amphitetras form a zigzag chain. 



Here, then, is an easy way of becoming acquainted in turn with the 

 principal fresh-water fossil and marine forms of some 84 out of about 

 1 10 genera mentioned by the Micrographics which, together with Mac- 

 donald's work on Water Analysis, I have taken as my guide, arranging 

 the genera, however, somewhat difterently, and picking out simply the 

 salient points, for some of which I have also consulted Carpenter and 

 Wolle's work. 



\To be continiied.\ 



Microscopy for Amateurs. 



By T. charters WHITE, 



QUEKETT CLUE. 



\^Co7itinued from page 9/.] 



Marine Objects. — No field of research so abounds in objects worthy 

 of attention as the sea-side, and here the student may make himself famil- 

 iar with marine fauna and flora to any extent, for the rocks and the algte 

 will furnish him with a variety of diatoms to be studied in their living 

 state, while on a calm warm day the surface of the sea will be found 

 teeming with the embryonic forms of many of the Crustacea. The 

 rock caverns at spring tides will well repay the search for diflerent 

 kinds of sponges, and various species of the Ascidia. The collecting 

 kit of the pond-hunter will suffice for many localities. In the rock 

 pools, deep down, he will find treasures in the shape of forests of liv- 

 ing Polyzoa, whose feathery forms he will soon learn to distinguish. 

 If these are attached to loose fragments of rock or pebble, they may 

 be traiisferred bodily to a jar of clean sea water, and will there live 



