1 882,] Zoology. 143 



the egg-capsules. These are in fact nothing more than killed dis- 

 torted protozoa of the genus Epistylis or Zoothamnium, clusters 

 of which I have frequently observed in the living condition on 

 the ends of the egg-capsules in fresh material presenting almost 

 precisely the appearance represented in Fig. 2 b c, of Gissler's 

 note. They are present or absent according as opportunity may 

 have been afforded for the protozoans to attach themselves, the 

 oldest capsules and those from which the embryos had escaped, 

 being the ones to which the Vorticellinae had most often affixed 

 themselves. At the time my note was written I did not think it 

 worth while to mention the occurrence of the protozoa which are 

 very common, the stalked forms especially. So numerous are 

 these, in places, that to estimate their occurrence at one hundred 

 per square inch of horizontal surface, we find the population of a 

 square rod to be nearly four millions (more exactly 3,896,800). 

 From what I have seen in the Chesapeake, this estimate, in many 

 localities, would be very low, from which it may be inferred that 

 the importance of the part played by the protozoa in the economy 

 of the world of life is, like that of the earth-worm, not yet appre- 

 ciated at its right value.— >. A. Ryder. 



Notes on Some Fkesh-water Crustacea, Together with 

 Descriptions of Two New Species.— Palamon ohionis Smith.— 

 (Palcemon ohionis. Smith, S. I., Freshwater Crustacea, U. S. 640; 

 Forbes, S. A., Bulletin Ills. Mus. Nat. Hist, No. 1, 5.) While 

 seining for fishes in the vicinity of Vicksburg, Miss., during the 

 past summer, I captured numerous specimens of this species. 

 The largest specimens were taken in the open river with a 

 small, fine-meshed, collecting seine. In some places they occur 

 in enormous numbers. On the 4th of July we were in Louisiana, 

 across the river from Vicksburg, seining in some ponds formed 

 m the making of levees along Grant's canal. At a single 

 draw of the net we brought out not less than a half bushel 

 of these river shrimps. Considering their size and abound- 

 ing numbers, they must constitute an important part of the food 

 of the fishes of these waters. They are captured for bait, and 

 are used to some extent for food ; and I can, from actual experi- 

 ence, testify that they are not to be despised by the hungry hun- 

 ter- My largest specimens agree exactly in size with those ob- 

 tained by Professor Smith from the Ohio river at Cannelton, Ind. 

 Many of the females were laden with eggs. The mandibles of this 

 species, as in the case of many other crustaceans, are not perfectly 

 symmetrical. The biting portions of the two mandibles are alike 

 and tridentate. The triturating process of each is long and 

 stands out at right angles to the body of the mandible. That 

 ot the left mandible is truncated at nearly right angles ; that of 

 the left is quite oblique, so that a dentated edge is presented to 

 «*e other mandible. Both molar surfaces are tuberculated. 



