68 PROCEEDINGS OF THE ACADEMY OP 



42. Eucampia zodiacus Ehr. Hab. Dredged by Mr. Powel, off rock at 

 Newport, R. I. Rare. 



43. Rbabdonema minutum Ktitzing. Hab. Narragansett rock, on algse. 

 Newport harbor, on algae, Mr. Powel. Stonington rocks, on algse. 



44. Cymbosira Agardhii Kiitzing. Hab. Rock off New Rocbelle. Ston- 

 ington Inlet. 



45. Tessella interrupt a. Kiitzing. Hab. Off rocks at New Rocbelle, on 

 algse. 



46. Amphitetras antediluviana Ehr. Hab. Mud from Black Rock 

 Harbor, along with Var. 0. On algse from New Rochelle. Mud from St. Mary's 

 river. Rice field, Savannah, mud. 



47. Biddulphia t u r g i d a . Hab. St. Mary's river, on algae. St. Augustine's 

 Quay, Florida. 



48. Isthmia nervosa Kiitzing. Hab. Riviere du Loup, St. Lawrence river, 

 on algse. L. I. Sound, fragments. Very rare. 



49. Bacteriastrum furcatum Shadbolt. Hab. Mud from St. Mary's river, 

 Ga., also on algse. St. Sebastian's river, on algae. Fernandina, Florida. Rice 

 field mud, Savannah river. 



Var. p. Without the bifurcate arrangement at the extremities. 



50. Bacteriastrum c vltv a, turn Shadbolt. Hab. Same localities as above. 

 Detected by Mr. Febiger in some mud brought by me from St. Mary's river, 

 marsh. 



51. Asterionella Bleakleyi W. Smith. Hab. St. Mary's river, on algje. 

 Fernandina wharf. Ogeechee canal. Savannah rice field mud, Savannah. 

 This species occurs in greatest abundance at St. Mary's, Ga. It differs slightly 

 from the specimens figured in Mic. Journ., in the outline of the valve, 

 which is more slender in the American variety, and also less inflated at the 

 base. I am of opinion that the normal number of frustules is four, which 

 may be increased to eight by subdivision, but in this latter case the persist- 

 ence of these is of short duration, two separate aggregations of four each re- 

 sulting, this being the largest number capable of cohering perfectly. A group 

 of four individuals undergoing subdivision is shown in Pi. II. f. 9, from rice field 

 mud. It may here be mentioned that Asterionella formosa and A. Ralfsii? 

 are occasionally met with in fresh water localities in this country. At a pond 

 on Longacoming, N. J., Mr. Powel made a gathering, containing both these 

 forms, along with a third, which differs so entirely from the described species, 

 as to entitle it to rank as a distinct one. The valves are only about three 

 times as long as broad, somewhat contracted in the centre. The strise are 

 indeterminate. Asterionella formosa occurs in the Delaware river, blue 

 clay ; also in mud from Cooper's creek. Diatoma stellaris of Bailey, 

 is no doubt referable to this genus. 



52. Plagiogramma Gregorianum Greville. Hab. Entire Atlantic coast, 

 L. I. Sound. At Black Rock Harbor, in mud and on algse. New London mud. 

 New Haven, Conn. Chesapeake Bay oysters. Rice field mud, Savannah. 

 Never in great quantity. 



The frustules of this somewhat doubtful genus vary very much in outline 

 and the vittse are often absent. 



53. Plagiogramma tesselatum Greville. Hab. Black Rock Harbor, in 

 mud. Very rare. Only a single perfect frustule has been found by me. 



54. Podosira Montagnei Kiitzing. Hab. Newport rocks, dredged by Mr. 

 Powel. 



[March, 



