REVIEW OF HIPPOCAMPUS — GINSBURG 585 



always septangular (incompletely novemangular in one out of 24 

 specimens). In other words, an extra plate for support of the dorsal 

 normally on last trunk segment only, infrequently also on first caudal 

 or penultimate trunk segment (on one side onl}^ of each one of two 

 specimens out of 24 examined); or, upper ridges of tail and trunk 

 normally overlapping on one segment only (with the exception 

 noted). Trunk segment 10 (in 23), sometimes 9 (in one specimen 

 from Campeche). Caudal segments usually 29 to 31, varying 28 to 

 32. Dorsal rays modally 11, varying 10 to 12. Pectoral rays modally 

 11, varj^ing 10 to 12. Base of dorsal on last two trunk segments. 

 Tubercles on upper ridge fairly well developed and pointed, some- 

 times low in full-grown males. Coronet comparatively liigh. Fila- 

 ments usually present, relatively not long, their numbers varying 

 greatly with individual fish and to some extent with age, sometimes 

 profuse and more or less branched, often absent or nearly absent, 

 especially in full-grown specimens; minute pimples usually profuse. 

 Color variously mottled with yellowish of contrasting intensity or 

 with brownish, without any definite color pattern; basal two-thirds 

 of dorsal with lengthwise rows of small diffuse spots, often more or 

 less coalescent, forming a diffuse network, sometimes nearly uniformly 

 pigmented but increasingly darker proximad; sometimes with a 

 distinct submarginal dark band, sometimes nearly hyaline. (See 

 table 5 for counts.) 



Measurements. — A male, 30.5 mm long, depth 18.5, snout 7, 

 postorbital 12, head 22.5, trunk 34, tail 62.5, and orbit 6 percent of 

 length. A female, 26.5 mm long, depth 17, snout 8.5, postorbital 13, 

 head 25.5, trunk 36.5, tail 55.5, and orbit 7.5 percent of length. 



Distinctive characters and relationships. — Tiiis species is evidently 

 closely related to zosterae. The greatest divergence is in the number 

 of dorsal rays, although there is a certain degree of intergradation 

 between the two species (see table 5). There is also a decided diver- 

 gence in the number of caudal segments, but the intergradation in 

 that character is even more pronounced than in the number of dorsal 

 rays. 



The individuals comprising the species regulus seem, from the ma- 

 terial examined, to form a comparatively homogeneous and compact 

 mass with reference to their structure, shown especially by the 

 relative stability in the number of trunk segments and the almost 

 constantly quadrangular first caudal segment. Of the 24 specimens 

 examined only one from Campeche has nine trunk segments, and 

 only one from Cat Island has an incompletely hexangular first caudal 

 segment. The specimens from Campeche otherwise differ but slightly 

 from those of the northern coast of the Gulf. The frequency distri- 

 butions of the fin rays in the Campeche lot correspond exactly to 



