Cidthj yiar'uia LahonUortj, St. Andrews. Jl 



on oacli side is moniliform. The first liooks are distinguislied 

 bv tlie great size of the main fang, ^\hieh has a crown of 

 small hooks above it — al)out three being nsnally visible in 

 lateral view, and l)y the comparatively small size and obTKinc 

 nature of the base, Mliich has above its dorsal angle an 

 abrupt incurvation, whilst on its anterior edge it has a sharp 

 point, for the attachment of a tendon, and a gentle incur- 

 vation beneath it. The modified form of tlnse early hooks 

 is indicated by the imperfect condition of those at the end 

 of the row. ]5y-and-by they form a donble row and 

 assume the typical condition in which the great fang is pro- 

 portionally less, the base less elongated, its lower edge more 

 convex, and the curve below the point on the anterior edge 

 less pronounced. About four small hooks are visible above 

 the great fang in lateral view. 



Polymnia nesidensis, Delle Chiaje, the sixth representative, 

 is a smaller spe< ies than TerebcUa ■nelmlosa and of a firmer 

 consistence, Avhich is found on both shores of Great Britain 

 and Ireland. The cephalic region has a less developed 

 dorsal collar than in T. nebulusa, and it is not usuallv folded 

 backward as in the speeie.s mentioned, and, moreover, no eyes 

 are present in many of the preparations. The upper lip in 

 front of this forms a large frilled process, and the lower lip 

 is also prominent. A median tongue-like process lies above 

 and internal to the latter. In extreme protrusion of the 

 mouth- parts some have the lower lip folded backward 

 veutrally with a smaller and larger fold above it, whilst in 

 others the lower lip projects downward and outward as a 

 cyathiform process marked by a fold at each side. 



The body is comparatively small as compared with 

 T. ne/mlosa, is convex and smooth dorsally, deeply grooved 

 veutrally from the ventral shields almost to tlie tip of tlie 

 tail, which in perfect examples has two longer median and 

 two lateral cirri on the ventral surface, the rest of the vent 

 being crenated or with short papilhe. The groove abuts on 

 two rounded lateral ridges, probably marking the ventral 

 longitudinal muscles, and biariiig the elevations or lamellae 

 for the hooks. The segments are two-ringed. Two segments 

 following that bearing the lower lip have a lamella at their 

 outer edges veutrally, and are opposite the first and second 

 branchiae. The anterior, indeed, olten stands out as a frill 

 on the front edge of the shield. In all, about sixteen shields 

 are present veutrally, and they bear traces of the two-ringed 

 condition of the segments generally. They are narrow and 

 transversely elongated in front, broad and transversely 

 shortened posteriorly. 



