95 



SOME PERFORATING AND OTHER ALG^ ON FRESH- 

 WATER SHELLS. 



By F. S. Collins. 



On August 24, 1895, Dr. W. A. Setchell and Mr. Isaac Holden 

 found, at Twin Lakes, Salisbury, Litchfield County, Conn., some 

 Unio shells, on which appeared to be quite a growth of algse. Mr. 

 Holden sent me some of the material, and after examining it, and 

 submitting some to Dr. E. Bornet, of Paris, I find the following 

 species represented, part of them perforating the substance of the 

 shells, part attached to the outside. 



Plectonema terebrans Born. & Flah. This was very abun- 

 dant all through the shells, and when the latter were decalcified, 

 formed a dense mat, which made it rather difficult to distinguish 

 the other algse that grew in company with it, I do not find that it 

 has been hitherto mentioned as occumng in this country, but Mr. 

 Holden reports that it is common in marine shells on the shores of 

 Long Island Sound, in company with Gomontia polyrhiza and the 

 other species usually found in marine shells. It is figured and 

 described in the Bulletin de la Soc. Bot. de France, xxvi, 158, PI. 

 10, figs. 5 and 6. The filaments are 1 to 1.5,a diam., flexuous, and 

 generally rather freely branched. 



Hyella fontana Huber & Jadin. This species also is new to 

 this country; it is scattered through the shells, sometimes in rather 

 dense, chroococcoidal masses, sometimes in loosely branching fila- 

 ments.- It is described and figured in the Journal de Botanique, 

 vi, 285. Like the Plectonema, it penetrates the interior of the 

 shells, but in the Twin Lakes specimens it is much less abundant 

 than the latter. 



Gomontia Hoidenii. Irregularly branched; cells with thick 

 walls, varying in shape, oval, cylindrical or polygonal; the terminal 

 cell cylindrical or tapering, not clavate; diameter of cells varying 

 from 12 to 50/^; sporangia (only once observed) ovate with elongate 

 base, about lOO/i long, 30/^ wide. In old shells of Unio. 



The large, mostly oval cells are quite distinct in appearance from 

 Erythea, Vol. V, No. 9 [19 September, 1897]. 



