246 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



pressure on the cover-glass tbey can be separated almost completely. 

 They remain, liowev^er, connected at the posterior end; ridge present. 



On longitudinal ("end") view the valves are seen to unite with 

 each other, eitlier by direct fusion and without appreciable line of 

 demarcation, or to be soldered by the thick interiorly projecting welt- 

 like ridge (in optical section, circular). 



Weltner believes that the tail structure (in this species) always con- 

 sists of a superior and an inferior half, each half being a process of the 

 corresponding valve. For, in the very few cases in which the valves 

 diverged posteriorly (remaining connected anteriorly), he saw this quite 

 plainly; with some shells the tail-halves were shorter; with others 

 longer; also inequality of length is very frequent in the same spore, 

 and one valve-process may be very long and the other very short. 

 Other spores have only one valve sharj^ly drawn out, the other showing 

 no trace of a tail. Tail thinner than that of M. psorospermieus (Lieber- 

 kiihn's figures in Biitschli). 



The spores in which the tail is double may lie in 3 positions:^ (1) 

 Most frequently the tails are plainly visible only on a transverse (or at 

 least an oblique) view. The tail-halves (which on vertical view cover 

 each other) then diverge. (2) With other spores things are different; 

 here the tail-halves appear side by side, on vertical view. (3) The third 

 position is that in which the tails cross (in the manner of a crossbill's 

 beak) both on vertical and transverse views. 



Capsules: 2, fusiform, length 5-1 to 5*9 //; their jjosterior end 

 bluntly rounded off and often obliquely truncated.^ The separated 

 capsules are rounded pyriform. Capsules mostly parallel-appressed, 

 mutually flattened. In spores whose capsules lie separated from each 

 other the granulated sporoplasm is seen between them. Longitudinal 

 ("end") views show the capsules to be imbedded in the sporoplasm. 

 Weltner only once certainly observed the sporoi)lasmic covering to 

 extend as far forward as the apex of the capsules. The latter is always 

 clear and glistening when containing the filament; dull when empty. 

 The capsule of the present form differs from that of M. psorospermicvs 

 (Lieberkiihn's figures in Biitschli) in shape ; also here the capsular index 

 is smaller. In M. schizurus the shape and position of the capsule is 

 also different. 



Filament: Not visible (under a power of 1,000 diameters) through the 

 capsular wall; only a dark shadow being seen. Exit produced by 

 glacial acetic acid ; also (spores in alcohol), by pressure on the cover 

 glass; the last method produced the extrusion of many filaments; 

 extruded filaments often quite straight; length, 47-9 //. 



> It seems to me that all this is produced merely by a slight lateral shifting of th*» 

 valves and by the flexibility of the tail. At any rate all these aspects are so produced 

 in M. cf. linearia (see p. 254). 



* A similar apparent marked truncation is an optical illusion in M. macrurua. 



