524 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
of fishes have been immature. In such positions they are usually 
inclosed in a membranous cyst, derived frdm the peritoneum of the 
host, and are provided with an extra epidermal investment which is 
often variously armed with spines. By a reference to figs. 54 and 74 of 
this paper it will be seen that this spine-bearing investment is some- 
thing entirely distinct from the true cuticle of the adult. In E. sagittifer 
there is a smooth epidermal investment which is easily stripped off. 
The spines in this species are borne on the true cuticle. (Fig. 80, 1c.) 
While it does not form a part of the plan of these notes to enter into 
details of structure, I have found it necessary in determining specific 
relations to make many series of sections, and have inserted a few 
sketches of the more characteristic features of the structure of the body 
wall of this somewhat anomalous group. In these researches I have 
incidentally confirmed many of Ssefftigen’s observations on E. proteus , 
and have found homologous characters in E. acus , E. attenuatus , etc. 
Systematic work in this group is attended with much difficulty, and 
I can not say that I am wholly satisfied with every identification which 
I have made in this paper. The older systematic literature contains 
only brief general descriptions of species, with usually no illustrations. 
It becomes a very perplexing matter, therefore, even in species of com- 
mon occurrence, where there are no strongly marked specific charac- 
ters, to refer them to old species. 
Again, it is to be noted that but little systematic work among the 
entozoa of fishes has been done on. this side of the Atlantic, and inas- 
much as the hosts, in a large number of instances, differ specifically 
from their European representatives, it should not be a matter of great 
surprise if their parasites should likewise present differences. 
I have endeavored to give in the descriptions and sketches of this 
paper the essential characters of the species discussed, whether regarded 
by me as new or referred to old species, so that subsequent workers in 
this little-cultivated field of research may not meet with the same diffi- 
culties I have encountered in determining species. 
Following is a list of the species described in this paper, with their 
several hosts : 
Parasite. 
1. E. acus (adult) 
E. acus (young) 
2. E. thecatus, sp. nov 
3. E. attenuatus, sp. nov . . . 
4. E. pristis 
var. tenuicornis 
5. E. incrassatus 
6. E. agilis 
7. E. serrani 
8. E. sagittifer 
9. E. carcharia> 
10. E. proteus 
Host. 
Prionotus evolans, Lophius piscatorius, Gadus raorrhua, 
Melanogrammus aiglefiuus, Pseudopleuronectes aineri- 
canus, Paralichthys dentatus, Roccus lineatus, Limanda 
terruginea, Cottus teneus. 
Stenotomus chrysops. 
Roccus americanus. 
Acipenser brevirostris. 
Tylosurus caribbams. 
T.ylosurus caribbseus, Lobotes surinaraensis. 
Lophius piscatorius, Paralichthys dentatus, Pomatomus 
saltatrix. 
Roccus americanus. 
Serranus atrarius: 
Cynoscion regale, Paralichthys dentatus, romatomus sal- 
tatrix, Serranus atrarius. 
Carcharias littoralis. 
Roccus lineatus, Cynoscion regale. 
