In 1925 Chapin reviewed the genera Syngamus and Cyathostoma and in the review described a new species of Syngamus which he had obtained from the American Crow, Corvus brachyrhynchos: this, he called Syngamus gracilis. It had been found in a bird from the Zoological Gardens at Philadelphia. He was of the opinion that this species had probably been recovered before from the American Crow but that its specificity had not been recognised. He assumes, in fact, that some if not all of the records of the occurrence of S. trachea in this species of host, and by inference probably in other Corvidae also, are incorrect and that S. gracilis is the species found. He bases this assumption on the physiological reactions of the parasite. It is a well known fact that S. trachea does not establish itself well in chickens and can in fact only reach maturity in young or very sick birds. The turkey is generally assumed to be the natural host of this helminth and Chapin is of the opinion that if S. trachea cannot establish itself satisfactorily in the chicken, then it is highly improbable that it can do so in the crow. For the chicken and the turkey are closely related phylogenetically, both being gallinaceous birds while the crow belongs to the Corvidae, which has no near kinship with the Galliformes.