180 TWELFTH A ]^N UAL REPORT. 



APPENDIX. 



The previous pages refer to the fresh-water Crustacea simply and 

 will give a tolerable idea of the variety exhibited in the fauna of the 

 lakes and rivers of America. The majority of Copepoda are marine 

 and the coasts of the United States will afford the student of 

 marine entomostraca a rich harvest of curious forms. These ani- 

 mals are now being investigated, it is understood, by competent 

 naturalists. In the meanwhile any notes may be of a temporary 

 interest. The following jottings, which are the result of a few days 

 stay on Mississippi sound, will give an idea of the fauna of the gulf 

 of Mexico. They are extracted from a paper offered the Minnesota 

 Academy of Natural Sciences. 



FAMILY CALANID^. 



Genus Pseudo-diaptomus. (Gen. n.) 



Resembling Metrida and Diaptomus; compactly framed; cepha- 

 lothorax 6-jointed, last two segments coalescent above; head round- 

 ed in front, beaked; eye small; antenofe appearing 22-jointed in 

 both sexes, longer than the thorax; the right male antennae genic- 

 ulate as in Diaptomus; an tennules bi-raraose, both rami rather short, 

 inner one seeming but two- or three- jointed; mandible ten-toothed; 

 maxillipedes well developed; feet all bi-ramose save the last, both 

 rami 3-jointed; first feet smaller; fifth feet with inner ramus obso- 

 lescent, in the male nearly as in Diaptomus, in the female rather 

 slender, simple, three-jointed; abdomen in the female 3-jointed, in 

 the male 5-jointed; stylets in the female longer; ova-sac single; 

 spermatophore pear-shaped. 



This genus is of unusual interest on account of its close approach 

 to the fresh-water section of the family. 



The spermatophore in this genus is large and swollen and, as 



