Silva Center for Phycological Documentation: Index Nominum Algarum

The INA is a card file and online reporting system maintained at the Silva Center for Phycological Documentation of the University Herbarium, University of California, Berkeley. It contains nearly 200,000 names of algae (in the broad sense). The BPU is a card file containing bibliographic references pertaining to algal taxonomy.
A working list of algal type specimens at UC is available here

Results from INA database

Fragilaria arcus(Ehrenberg) Cleve Bih. Kongl. Svenska Vetensk.-Akad. Handl. 24(Afd. III, 2): 9 1898
Fragilaria arcus(F.T. Kützing) Cleve image
Fragilaria arcus var. amphioxys_('amphiozys')(Rabenhorst) A. Cleve-Euler Kungliga Svenska Vetenskapsakademiens Handlingar, ser. 4 4{1}: 54 1953
Fragilaria arcus var. rectaCleve image