REVIEW OF HIPPOCAMPUS — GINSBURG 549 



nearly the same as in guttulatus and unlike that of hudsonius (see 

 discussion on p. 544), but in the available specimens of europaeus 

 the color is not sufficiently well preserved to determine this difference 

 more definitely. 



The relationship of europaeus to the other species and subspecies 

 of Hijjpocampus nearest it is quite obscure and may be interpreted 

 in more than one way, depending on the assumption made at the 

 start. In its short snout europaeus agrees closely with hippocampus 

 from the Mediterranean, but in the counts of the caudal segments 

 and dorsal and pectoral rays, as well as in the relative development 

 of the tubercles, it is about intermediate between hippocampus and 

 multiannularis. If we assume that europaeus is the more primitive 

 form, it may follow that hippocampus and multiannularis diverged 

 from it in different directions, one in the direction of having fewer 

 fin rays and caudal segments and the other in the direction of having 

 higher counts of the same characters. Also, hippocampus diverged 

 in the direction of the tubercles becoming obsolescent, retaining the 

 primitive condition of the short snout of the parent species; while 

 multiannularis diverged in the direction of an increasing length of 

 snout and a better development of the tubercle. 



Again, we may assume that multiannularis is the more primitive 

 form and argue that europaeus diverged from it in the direction of a 

 diminishing number of segments and fin rays, a decreasing promi- 

 nence of the tubercles, and a decreasing length of snout. As a 

 further intensification of this same developmental tendency, it may be 

 argued that hippocampus developed from europaeus. Or we may 

 assume that hippocampus, or guttulatus, or hudsonius from the 

 American coast is the more primitive form. In fact, each assump- 

 tion will lead us to a different interpretation of the close relation- 

 ship of these species and subspecies. The apparent relationsliip 

 of europaeus to guttulatus, to hudsonius, and to hippocampus seems 

 to indicate that europaeus is the more primitive form and that with 

 it as a focal center the other three species diverged in different di- 

 rections, but the evidence does not justify the unquestioned 

 acceptance of this. 



Marked features of europaeus are the decided tendency shown 

 by the penultimate trunk segment to have an extra plate on top 

 and the frequency of occurrence of 12 trunk segments. These fea- 

 tures are shown also by ingens and to a much more pronounced 

 degree than by europaeus. They also may indicate a more primitive 

 condition. 



Material studied and geographic distribution. — La Rochelle, France 

 (28544, the type; 93217 and 21122). Also two specimens v/ithout 

 certain locality but evidently belonging to europaeus (16454); they 



