NO. 3582 GENUS ENTOMACRODUS — SPRINGER 5 



obvious is assumed to be present when a space exists between the 

 spinous and rayed portions of the fin greater than that separating the 

 11th and 12th dorsal spines. 



Dorsal fin rays: A count of tlie bases of the segmented rays. 



Anal fin rays: Two methods of counting tlie segmented anal rays 

 are employed, method A and method B. In most specimens of most 

 species the terminal "ray" consists of two elements, the posteriormost 

 considerably reduced, closely applied to the next element anterior 

 and difficult to see. Radiographs or skeletal preparations show that 

 these two elements are supported by a single proximal pterygiophore; 

 this condition is called "S" (spht through base). In another condi- 

 tion (typical in some species), the terminal ray is removed from the 

 next element anterior and the terminal proximal pterygiophore 

 supports a single segmented ray; this condition is called "N" (not 

 split). In method A counts, the split and unsplit conditions are 

 not differentiated. Thus the two terminal elements, if supported by 

 a single pterygiophore, or the terminal element, if supported sepa- 

 rately, are counted as one. In method B counts, split elements are 

 tallied as two. Method B counts, of course, will result in higher 

 averages than method A counts. In those species which typically 

 exhibit the S condition, individuals with counts one ray more than 

 the modal value (using method A) usually prove to be of the N type. 

 What has happened, then, is that a pterygiophore has been added at 

 the end of the fin, and where the terminal pterygiophore normally 

 supported two elements, the posteriormost element has become 

 associated with the added pterygiophore (or conversely, a pterygio- 

 phore was lost and the posteriormost element has become associated 

 with the next pterygiophore anterior). Determination of the N or 

 S condition may be difficult with some specimens. I have checked 

 several hundred of my determinations made externally on specimens 

 with radiographs of the same specimens and found my error to be 

 less than one percent. 



The question arises as to which of the anal fin ray counts should 

 be used for systematic purposes — method A or method B. In other 

 words, should one count pterygiophores or fin rays? Unless otherwise 

 noted, anal fin ray counts reported herein refer to method A counts. 

 Method A counts are simplest to make, are those which have generally 

 been employed in the literature of salarine blennies, and are the ones 

 naturally made when uninstructed individuals count anal fin rays of 

 salarines. Investigators who try to determine ecological effects on 

 anal fin ray counts of salarine blenniids should test their data for 

 both method A and method B type counts. 



Vertebrae: Total count of centra including that of hypural vertebra, 

 taken from radiographs. The caudal vertebrae are those which 

 bear a haemal spine. 



