I have found Sphenomonas quadrangularis so far only in the Simmelried, where the species occurs, however, only sporadically. Sphenomonas quadrangularis can be identified by the 4 straight, longitudinal ridges, which are arranged quadratically in optical cross-section (s. fig. 3 d). In addition, Sphenomonas quandrangularis is conspicuous by a hyaline, gelatinous body, mostly localized in the posterior half of the body. This hyaline body has already aroused the interest of the first observers. It is insoluble in both alcohol and ether (i.e. no oil or fat). In water, sodium hydroxide and ammonia the body swells but does not dissolve. It is thought to be a high molecular weight reserve of unknown nature. Sphenomonas quadrangularis has two flagella. The flagellum used for locomotion can reach twice the body length (s. fig. 2 b). The trailing flagellum, on the other hand, is very short and is often overlooked, especially when it fits closely to the body between the longitudinal ribs (s. fig. 2 a).