8 McMURRICH 



musculature of the disk is ectodermal and but moderately de- 

 veloped. The stomatodaeum is provided with well-marked 

 longitudinal ridges, and in all the six specimens which were ex- 

 amined with regard to this point tivo siphonoglyphes were present. 



In all the specimens examined, with a single exception, there 

 were six pairs of perfect mesenteries, two of these being direc- 

 tives. In the majority of the specimens there were altogether 

 five cycles of mesenteries, that is to say ninety-six pairs, but in 

 some there were only four cycles and occasionally the fifth 

 cycle was only imperfectly developed. In the exceptional 

 specimen referred to above, there were only four pairs of per- 

 fect mesenteries. Two of these were directives, and between 

 these two pairs on one side there were two pairs of perfect 

 mesenteries, but none on the other. In other words, the irreg- 

 ularity affected only one-half of the specimen. In the normal 

 half there were five cycles of mesenteries represented, the me- 

 senteries of the fifth cycle, as is usual, lacking mesenterial fila- 

 ment. In the irregular half the various cycles could not be de- 

 termined accurately, but judging from the relative breadths of 

 the mesenteries the arrangement was D-iv-iii-iv-ii-iv-iii-iv-iii-iv- 

 D, the mesenteries of the fifth cycle being omitted in this count. 



The longitudinal muscles of the mesenteries were fairly well 

 developed, forming a moderate thickening upon the inner por- 

 tion of the primary mesenteries as represented in Fig. 4. Oc- 

 casionally the pennon was somewhat narrower and more promi- 

 nent, this condition being apparently normal for the directive 

 mesenteries, the pennon in these having the form represented in 

 Fig. 5. Parieto-basilar muscles are hardly at all developed 

 (Fig. 4), and the basilar muscles have the form described by 

 Carlgren, though not usually as large as those he has figured. 



In only two specimens of those examined were reproductive 

 organs present ; in these they were borne upon the mesenteries 

 of the second, third and fourth cycles. Acontia occurred and 

 both the inner and outer stomata were found in the perfect 

 mesenteries. 



The specimens here described are undoubtedly identical with 

 those described by Verrill ('65 and '69) as Metridiiim fimbria- 



