254 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



Shell consisting of 2 valves, superior and inferior in position; ridge 

 present, fornung continnation of tail. The tail in this species is a 

 shell ])r()cess, consisting of 2 halves, a superior aiul an inferior, eacli 

 connected with and forming a solid process of the corresponding valve. 

 Length of tail, 38 ;/ . Valves separating very slowly in sulphuric acid 

 (cold, concentrated), the gradual lateral shifting of one valve over 

 another beginning witiiin a few minutes aud continuing for 20 or 30. 

 Coincidently the two tail halves diverge, serving well as indices of the 

 amount of lateral sliifting of the valves. Iodine fails to loosen the 

 coniu^etion of the tail (or of eitlu^A' half) with the valves. 



Capsules long, narrow, parallel-api)ressed ; capsular index about O-IO ; 

 walls rendered transpiuent and filaments visible by iodine water. 



Sporoplasm showing the usual anterior extension of the supero- 

 medinn cornu. The other cornua are also recognizable. Vacuole pres- 

 ent, subcircnlar in outline, usually placed toward the anterior end of 

 the sporoplasm. As regards nuclei, hydrochloric acid alcohol carmine 

 always stains as many as and usually 2, rarely 3; position inconstant, 

 one or both being either before or behind the vacuole. In addition, 

 tliere are constantly present, at or close to the extreme posterior end 

 of the sporoplasm, 2 deeply stained dots, which are too minute to show 

 any structural details. 



Hahifdt. — 7 or 8 cj^sts at bases of the spines of the second dorsal fin 

 of Ameiitrus melas Enf (bulUiead) from Storm Lake, Iowa, collected 

 August 23, 18D0,by Prof. Seth E. Meek, to whose kindness I am indebted 

 for the specimen. 



This species can only be compared with the next. The following 

 summarizes Miiller's scanty diagnosis of tluit form: 



Body very narrow, 3 to 4 times as long as broad; capsules parallel- 

 appressed; tail simple, occasionally double. 



The present species answers to all of these characters, but they are 

 too few to warrant the fusion of the two forms, although their identity 

 may be strongly suspected. If established, their identity would con- 

 stitute a very interesting fact, both in zoological and in geographical 

 distribution, for we should then have a species found (so far) confined 

 in its zoological range within the Siluridce and with a very wide geo- 

 graphical distribution.' 



'For the geographical distribution (in South America) of i?.sp&(T and of P.fasc'iaium, 

 see Eigenmann & Eigenmann, Revision So. Amer. Neinatognatbi (Occas. Papers Calif. 

 Acad. Sci., San Franc, 1890), pp. 123, 209. Considering the names used hy Miilh^r, 

 the date of his writing, etc., it seems rather probable that his k)calitios were those 

 known to Cuvier aud Valenciennes (1840), viz, for 7?. scbo',, Surinam, Cayenne, Rio 

 Janeiro, Bnenos Ayres, and for P. fasciatum,, Sin inam. 



