410 DR. A. H. COOKE ON THE 



Group 4. Subgenus jStrigatella Swainson. 



This group shows : — 

 acuminata S. 60 + nasc. vows of teeth, 6 cusps on rhachidian. 



astricta 55 ,, ,, 7 ,, ,, 



colnmbellceformis 75 ,, ,, 5+ ,, ,, 



limb if era 86 ,, ,, 7 ,, ,, 



litterata 76, 80, 86, 87 ,, ,, 7 ,, ,, 



luctuosa 81 ,, ,, 7 ,, ,, 



pellis serpentis 52 ,, ,, 7 ,, ,, 



planilirata 95 ,, ,, 6 ,, ,, 



tristis 74 ,, ,,8 ,, ,, 



Rhachidian tooth shaped more or less as in Mitra pi'oper, 

 with 5-8 narrow cusps, sharp or blunt, short or prolonged, the 

 two external somewhat withdrawn and obscure : laterals comb- 

 shaped, the inner half of the framework more or less arched, the 

 outer half straight, with a marked "break" or division between 

 the two halves ; inner half set with well-marked smallish cnsps 

 (the inner 3 or 4 incline slightly inwards), which become mere 

 points or fade away altogether on the outer half ; extreme end 

 usually quite bare. 



Text-figure 6. 



Lateral and rhacliidian tooth of Strigatella litterata Lam. 



1. S. acimiinata Swains. Rotuma. Rhachidian 6-cusped, the 

 4 central cusps deeply rooted, the 2 outer small, and lying at the 

 side and somewhat behind • cnsps rather thick, projecting well 

 above the upper margin : laterals with 7-8 well formed, deeply 

 rooted cusps, these I'apidly diminish to mere serrations or points ; 

 there are about 10 of these, reaching almost to the end ; the 

 "break" not very prominent. 



An immatiu-e specimen at Cambridge, also from Rotuma, 

 lias 5 cusps on the rhachidian, the central the longest, and fewer 

 cusps on the laterals. 



2. S. astricta Reeve. Maui. Rhachidian 7-cusped, the 2 outer 

 obscure, lying as in aciimiinata, central the largest, all deeply 

 rooted, not projecting far beyond the margin ; base scarcely 

 arched : laterals with 6 inner denticles, conspicuous, deeply rooted, 

 then suddenly mere seriations, or the rest quite bare ; 4th ciisp 

 from inside the largest ; "break" conspicuous. 



3. »S'. columhellaiformis Reeve. Rotuma,. Rhachidian squarish, 

 5-cusped, with an additional obscure cusp or projection at the 

 sides, cusps \eYj deeply cut and chiselled out of the mass, tips 

 blunt, scarcely projecting above the margin : laterals with 6-7 



