1903.] NATURAL SCIENCES OF PHILADELPHIA. 799 



but little is known. From all of the species which have been accurately 

 described, with the single exception of that to which Greeff has given 

 the name of T. helgolandica, the Massachusetts form is clearly differ- 

 entiated. 7'. helgolandica it resembles closely in all of those technical 

 characters, such as the distribution of rosette-organs and parapodial 

 fin glands, the form of the parapodia, relative length of the cirri, etc., 

 which have lx?en most relied upon for the discrimination of species by 

 the best students of this group — Apstein, Greeff and Vejdovsky. 



On the other hand there are many minor points of difference, most 

 of which are constant in the 8 specimens at hand, but which are of such 

 a nature that they may be temporary or local, and not specific. The 

 specimens vary in length from 6 mm., in one having 10 pairs of para- 

 podia, to 18 mm., in one having 16 pairs of parapodia besides a caudal 

 appendage of 3 mm. on which occur 8 additional pairs. These and the 

 intermediate growth stages exhibit the changes in the proportions of 

 cirri, etc., which have been described by Carpenter and others. In all 

 except the largest example the rosette-organs are limited to a single 

 one situated in the broad fin membrane near the apex of each ramus 

 of the foot, exactly as in T. helgolandica, but the largest specimen only 

 possesses the third one on the anterior side of the base of the neuropodia 

 of the first and second feet, generally present in that species. In these 

 the dorsal ramus of the parapodia (fig. 13) is the longer, while T. 

 helgolandica is always figured as having the ventral ramus longer. The 

 fin membranes and the neuropodia! gland exhibit no differences. The 

 4th and 5th jmrapodia are the longest, and all except the first two have 

 their finned ends turned sharply caudad. Differences in the shape of 

 the prostomivmi, which has a more slender median part and longer 

 horns, in the shape of the base of the second pair of cirri, which has 

 an anterior shoulder, and a longer interval between the second pair 

 of cirri and the first parapodia may be due to a different state of con- 

 traction of the preserved specimens. In all, excepting the second, 

 of these respects the resemblance to the figures of 7\ rolasi Greeff is 

 closer. The Woods Hole specimens were collected by Mr. Edwards, 

 and were studied only after preservation in formaline, but no red or 

 yellow pigment was apparent. The Crab Ledge specimens while alive 

 had no red pigment, and the central body of the rosette-organs was 

 brown and not yellow; moreover, these organs appear to have a less 

 regular structure than in T. helgolandica, Ijut for the study of these, as 

 well as the lenses of the l^lack-pigmented eyes, and the brain, fresh 

 material is required. 



In all of the specimens the alimentary canal largely fills the coelom, 



