214 SYSTEMATIC ARRANGEMENT 



** Tentacles retractile. 



3. Thecacera. 



Body limaciform, smooth. Mantle obsolete ; forehead with a 

 slight plain veil. Tentacles two, broadly laminated, retractile ; 

 sheaths moderate, smooth-edged; branchial plumes non-retractile, 

 with a single row of small tubercles round the branchial region. 

 Lingual membrane with twelve or fourteen plates, the two inner 

 plates on each side with a bicuspid spine ; no central plate ; lateral 

 jaws small, corneous. 



1. T. pennigera, t. 236. f. 3. 



2. T. virescens, Alder fy Hancock, Ann. fy Mag. Nat. Hist. 1851, 



viii. 290. 



c. Lingual membrane broad, with many series of teeth (p, 213). 



Fam. V. TRIOPID.E. 



Lingual membrane broad. Teeth in numerous longitudinal rows, 

 equal, or the two inner of each tide larger ; no central plate ? Body 

 depressed. Mantle obsolete, covering the head with linear or sub- 

 clavate marginal beards. Dorsal tentacles within retractile ; sheaths 

 laminated. Gills not retractile. 



* Dorsal tentacles laminated. Teeth unequal. 



1. Triopa. 



Body depressed. Mantle small, covering the head, with marginal 

 appendages. Dorsal tentacles laminated, with slight sheaths ; oral 

 tentacles cylindrical. Branchiae not retractile. Lingual membrane 

 rather broad. Teeth numerous, two innermost with large spines ; 

 central plate none or square. 



1. T. claviger, t. 67. f. 1, 2, t. 274. f. 1 ; Forbes fy Hartley, B.M. 

 t. A.A.A. f. 1. Far. T. plumosa, t. 231. f. 2. 



" Central tooth of Triopa claviger none ; lateral teeth 8 ; first 

 slender, elongated, curved ; second wide, hooked, bimucronated at the 

 tip ; the others squarish, laminaceous, lying upon each other." — 

 Lovdn. 



" Central tooth of Triopa lacer laminaceous, flat, squarish, ob- 



Fig. 117.— Teeth of Triopa lacer. 



lique; lateral teeth 8, dissimilar; the iiist elongated, from an oval 



