18 THE APODOTTS irOLOTHUKIANS 



group, the genera are so closely allied. Of the 10 genera which have been pro- 

 posed, six are universally accepted: Ankyroderma, Caudina, Eupyrgus, Haplo- 

 dactyla, Molpadia, and Trochostoma. Embolus Selenka is now regarded only as 

 a synonym of Trochostoma; Echinosoma Semper corresponds to Eupyrgus; 

 Microdactyla Sluiter is best treated as a synonym of Caudina; and Liosoma 

 Brandt (Lioderma, Bronn), used by Stimpson for a Trochostoma, is really 

 a synonym of Chiridota. But generic limits in this family are not sharply 

 drawn and the evidence now to be presented breaks down all possible distinc- 

 tion between Ankyroderma and Trochostoma. As generally denned, the former 

 is distinguished from the latter by the presence of rosettes of racquet- shaped 

 rods, from the center of which there extends outward a conspicuous anchor. 

 These anchors have a long shaft and serrate flukes, so that if they are nu- 

 merous, the body surface is very rough, and it is not remarkable that Anky- 

 roderma has been considered a clearly denned genus. I have had the oppor- 

 tunity of studying more than 350 specimens of these two genera, and a careful, 

 long-continued examination has convinced me that the presence of the anchors 

 and rosettes of racquet-shaped rods cannot be regarded as even a constant 

 specific character. The first intimation I received of this fact came when com- 

 paring some specimens of "Ankyroderma danielsseni Theel" with others which 

 I had identified as " Trochostoma violaceum (Studer)." I was struck by the 

 similarity in general appearance and in the calcareous deposits of the body-wall, 

 and my faith in the distinction between the two genera was shaken when I found 

 some of the racquet-shaped rods in a specimen of what I had called Trocho- 

 stoma. This led me to make numerous preparations from nearly all the speci- 

 mens, and the longer I compared them, the more I became convinced that they 

 all belong to a single species. Some are perfectly distinct specimens of T. vio- 

 laceum, and show not a trace of anchors or racquet-shaped rods, and others 

 agree perfectly with Theel 's ('860) description and figures of A. danielsseni. 

 Between these two extremes, however, there are several specimens which at 

 first sight would pass for T. violaceum, but of which a careful examination 

 shows that here and there are scattered more or less imperfect groups of 

 racquet-shaped rods, and occasionally there is evidence of an anchor having 

 been present. My suspicion that Ankyroderma was untenable was thus con- 

 firmed, but it was made a certainty when I came to study the 150 or more speci- 

 mens of Ludwig's T. intermedium. These varied in length from 17 to 180 mm. 

 and showed all sorts of intermediate stages in the condition of the racquet- 

 shaped-rod rosettes. The smaller specimens (those under 60 mm.) all have a 

 very thin skin in which the colored bodies are light yellowish brown and the 

 rosettes with anchors are numerous. They are clearly Ankyrodermas and I at 

 first supposed they represented a new species of that genus. The largest speci- 

 mens (those from 100 mm. up) have the body-wall rather thick and firm, the 



