INTRODUCTION. 



The following pages are chiefly the result of a few_ days' collecting excursion in 

 Mobile bay and vicinity and, of course, give but a very partial idea of the fauna of the 

 littoral zone of the Gulf of Mexico. It is much to be regretted that a careful study of 

 the fauna of the gulf is not now. possible. The Crustacea especially, if exhaustively 

 studied, would be expected to afford answers to many interesting biological questions. 

 Enough is even now known to stimulate curiosity and afford some valuable clues. There 

 have been found several genera new to science, one of which finds its nearest affinity in 

 an Australian species, but unexpected agreements are often quite as instructive as new 

 varieties. Alabama is remarkably rich in novelties in her fresh-water carcinological 

 fauna, despite the rather conspicuous poverty of material. 



A great deal of attention is just now being given to the careful elaboration of local 

 faunae, notably of isolated or peculiarly situated bodies of water. Such investigations, 

 if carried on in the comparative spirit, are powerful aids to the intelligent comprehension 

 of those natural laws most directly involved in the correct elucidation of the develop- 

 ment and differentiation of animal and vegetable life. And many times the simpler 

 structure and less complex conditions found in lowly and inconspicuous groups of organ- 

 isms afford just the opportunity needed to deduce principles whose practical application 

 is found in the higher and economically valuable groups. Nor is the possibility of secur- 

 ing results of direct economic importance excluded at the beginning of such an investi- 

 gation, as has often been demonstrated. A very simple illustration is found in the oc- 

 currence of the embryonic stages of parasitic worms in the micro-crustacea of pools and 

 rivers in Alabama, not to mention the fact that similar minute Crustacea afford the essen- 

 tial food supply of the fry of many food fishes. Should this paper serve to stimulate stu- 

 dents to cultivate this interesting field by directing attention to the sources of informa- 

 tion and the nature of the material, he will be abundantly repaid for the annoy- 

 ance of the most trying excursion yet attempted. The fresh and salt waters of 

 Alabama are inhabited by numerous species of nine orders of Crustacea, as follows : 



The Ostracoda or shelled Crustacea, are survivers of one of the oldest groups, oc- 

 curring abundantly in lower Palaeozoic strata, and preserve much of the primitive sim- 

 plicity of structure. These animals are rarely of conspicuous size, appearing more fre- 

 quently as mere animated specks, and are found in marshy or oozy situations,. especially 

 in small pools and estuaries. The ocean is the home of a great number of species some 

 of which are of considerable size. Mobile bay furnishes the largest species yet found 

 in America. This is, however, a member of the strictly fresh-water genus Cypris. The 

 great depths of the ocean contain their own representatives of this order. 



The Cladocera are likewise minute bivalved Crustacea, but in this case only the thorax 



