Gatty Marine Laboratory, St. Andrews. 11 



on eacli side is moniliform. The first hoolcs are distinguished 

 by the great size of the main fang, which has a crown of 

 small liooks above it — about three being usually visible in 

 lateral view, and by the com])aratively small size and oblique 

 nature of the base, whicli 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 these early hooks 

 is indicated by the imperfect condition of those at the end 

 of the row. By-and-by they form a double 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 species than Terebeila riebulosa and of a firmer 

 consistence, which is found on both shores of Great Britain 

 and Ireland. The cephalic region has a less developed 

 dorsal collar than in T. nebulosa, and it is not usually folded 

 backward as in the species mtntioned, 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 })rocess lies above 

 and internal to the latter. In extreme protrusion of the 

 month- parts some have the lower lip folded backward 

 ventrally with a smaller and larger fohl 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. nebulosa, is convex and smooth dorsally, deeply grooved 

 ventrally from the ventral shields almost to the tip of the 

 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 ])api]](e. The groove abuts on 

 two rounded lateral ridges, probably marking the ventral 

 longitudinal muscles, and bearing the elevations or lamellse 

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

 following that bearing the lower lip have a lamella at their 

 outer edges ventrally, and are opposite the first and second 

 branchiae. The anterior, indeed, often stands out as a IVill 

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

 are present ventrally, 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. 



