MUSEUM OF COMPARATIVE ZOOLOGY. 265 



be young specimens of a species of true Stolonoclypus, to judge by analogy 

 with the young of this Florida species, which undergo very great changes 

 durino- their growth, resembling to such an extent Echinocyamus pusillus 

 Leske of Europe, that for some time I considered the young as identical 

 with that species. 



Littoral to olb fathoms. 



Stolonoclypus Ravenelii A. Ac, nov. sp. 



The presence of a true Laganum in the West Indies has been often men- 

 tioned by various writers on Echinoderms, but it has invariably been pre- 

 sumed to be founded upon mistaken localities (Rumphia Lesueuri) or a 

 confusion with young specimens of Stolonoclypus prostratus. Mr. Pourtales 

 has dredged, from a depth of thirty-four fathoms, a small Clypeastroid of about 

 two inches in length, which has the facies of a Laganum to such an extent 

 that it would pass for one without an examination of the internal structure. 

 The outline is pentagonal, with rounded corners ; the pentagon is equilat- 

 eral, and more regular than in any spacies of Laganum, the central part 

 of the test rising abruptly from the extremity of the ambulacral rosette. 

 The test has a thick, rounded edge, and it may be that specimens of this 

 species have been collected by those who have referred to the presence of 

 a Laganum in the West India Islands. Hupe speaks of Laganum latissimum 

 as found on the coast of Brazil ; it certainly cannot be the Clypeaster 

 latissimus Lam., which Agassiz distinctly says is allied to C. scutiformis, 

 although by mistake it was subsequently referred to Laganum in the 

 Catalogue Raisonne, and which is found in the East Indies. The specimen 

 collected by Mr. Pourtales is evidently the young of a large Stolonoclypus 

 collected by Mr. Ravenel off Charleston Harbor, which, from want of 

 additional material, remained undescribed in the Museum collection. It 

 does not differ in outline (.although measuring five and a half inches in 

 length) from the smaller specimen ; has the same thick, rounded edge, with 

 abruptly rising test near the extremity of the ambulacral rosette. The 

 rosette is not raised as in other species of Stolonoclypus, but is flush with 

 the rest of the test ; the whole lower part of the test is flat, as in Laganum. 

 In the smaller specimen the rosette is harp-shaped, well opened at the 

 extremity, as in Echinarachnius, while in the adult this is the case only in 

 the anterior ambulacrum ; the others are brought close together at the ex- 

 tremity. The ambulacral rosette extends to within one third the distance 

 of the apex from the edge. The poriferous zone is much broader than in 

 S. prostratus. The furrows are more numerous and more closely crowded 

 together than in any other species of Stolonoclypus. In the younger speci- 

 men the lower surface is covered with spines only upon the interambulacral 

 31 



