NATURAL SCIENCES OF PHILADELPHIA. 239 



Plumieri, Block,) Decapterus, Blkr., BlepJiarichthys, Gill, Aiectis, Raf. (= Gal 

 /us, Lac, = Gallichthys, C, == Scyris, C.,) Hynnis, Cuv., Argyriosus, Cuv.. 

 Selene, Lac, Voiner, Cuv., Chloroscombrus, Grd., Elagatis, Bennett, (= /->e- 

 captus, Poey,) Zonichthys, Sw., Naucrates, Raf., Trachi/notus, Lac and Elacate. 

 Cuv., but the latter probably represents another family. Next to Elacate 

 follows the family of Echencidoidce. 



Prof. Poey, believing that there were two groups of Echeneioids charac- 

 terized by differences of dentition, homodont and isodout, has invited me 

 to name and describe them as genera.* I cannot, however, regard thos 

 variations as indicative of generic distinction, nor as coincident with any 

 other peculiarities which would entitle the homodont and isodont species to 

 be genetically distinguished, the differences being simply very slight dif- 

 ferences of degree. 



The Echeneioids appear, however, to form two very distinct groups of 

 higher value than genera, each of which is again divisible into two others, 

 which appear to be true genera. They are recognizable as follows : 



I. Body and tail slender and subcylindrical. Ventral fins 



with their inner rays more or less connected by a 

 membrane which is partly free from the abdomen ; 

 pectorals angulated ; caudal with the median rays pro- 

 duced in the young, emarginated in the adult. Lower 

 jaw with a cutaneous symphiseal projection Echeneides. 



.' Discal lamina? 21 26," (A', naucrates, L.) Echeneis. 



0. Discal laminae 10 11, (E. linedta, Menz.) Phtheirichthys. 



II. Body and tail robust and compressed. Ventral fins with 



the inner rays more or less attached to the abdomen, 

 and folding in an abdominal depression ; piectorals 

 rounded ; caudal generally more or less emarginated 

 in the young, as well as in the adult. Lower jaw with 



no flap Remorje. 



*. Discal laminae 12 19, (E. remora, L.) Remora. 



(J. Discal lamina? 27, (E. scutata, Gthr.) Remilegia. 



If the principles of Dr. Gimther are correct, all the forms described by Prof. 

 Poey would be probably referrible to five known species. That gentleman 

 and Sir John Richardson have demonstrated that the form of the caudal fin 

 (only, however, to any extent among the typical Echeneides) varies with 

 age ; consequently divisions based on the outline of that fin are illusive. 

 The species described by M. Poey would be referred by Dr. Giinther to the 

 following species ; the figures in parenthesis indicate the respective size of 

 the fishes on which M. Poey founded his several species : 



1. Echeneis naucrates, Lin. =E. guaican, P. (800 mill.) = E. metaliica, P. 

 (600 mill.) 



2. Echeneis albicauda, Mitchill = (E. holbrookii, Gthr.) = E. verticalis, P. 

 (half grown, 380 mill.) 



3. Phtheirichthys lineatus = E. apicalis, P. (260 mill., half grown) == E. 

 sphyrsenarum, /'. (75 mill., very young.) 



on each palatine bone, and in another thirteen inches long, a narrow band of villiform 

 teeth on the same bones, while Dr. Holbrook asserts, that in a specimen nine inches 

 long, he found a " small patch of minute teeth on the vomer, and a small, narrow group 

 of similar teeth on each palate-bone." M. Poey denies to his C. keteropygus (winch I 

 am unable to distinguish from the C.falcatus) any palatal teeth. Are the palatal teeth 

 then deciduous and lost with age, but still more or less persistent in different individuals ' 

 Such is probably the case. 



* M. Poey has since communicated to me his discovery of the more or less heterodont 

 dentition of all ihe species of the family known to him. 



1862.] 



