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approach to the other members referred to that subfamily. True, the oral cone 

 is not terminated in a sucking disk, like that found in the typical genus Para- 

 doxostoma; but in another genus, Paracytherois, recently established by G. W. 

 Miiller and unquestionably belonging to the present subfamily, there is likewise 

 no trace of any sucking disk on the oral cone; and the presence of such a 

 disk cannot of course be regarded as an exclusive character of the subfamily 

 Paradoxostomince. 4 genera referable to the present subfamily will be treated 

 of in the sequel. A 5th apparently distinct genus, Machairina (Xiphochlhis) 

 Brady, may be here named; but this genus is as yet only known, as regards 

 the shell. 



Gen. 49. Sclerochilus, G. O. Sars, 1865. 



Generic Characters. Shell compressed, more or less elongate in shape, 

 and of rather firm consistency, with the marginal zone highly chitinised. Sur- 

 face of valves smooth, without any obvious sculpture. Hinge imperfect. Eyes 

 coalesced. Anterior antennae with the terminal part 5-articulate and clothed 

 with long and slender setae, forming a dense apical fascicle. Posterior antennae 

 robust, with the penultimate joint distinctly subdivided, but without any seti- 

 ferous ledge in front, apical claws 3 in number, one of them reduced in male; 

 flagellum slender, with the knee about in the middle, vesicle leading to it large, 

 bifurcate. Oral cone projected obliquely forwards and obtuse at the tip, with 

 the 2 lips well defined. Mandibles with the masticatory part narrowly produced 

 and scarcely at all incurved, cutting edge very oblique and finely denticulated, 

 palp slender and imperfectly jointed, with the vibratory plate narrow, trisetose. 

 Maxillae with the basal part rather prolonged and apparently composed of 2 

 distinct segments, the distal one conically tapered, terminal part rather defective, 

 only exhibiting a single narrow, unisetose masticatory lobe inside the palp, 

 the latter indistinctly jointed, with 2 curved apical setae; vibratory plate narrow 

 lanceolate in shape, with 2 or 3 thin deflexed setae at the base. Legs com- 

 paratively short and stout, with each of the tirst 2 joints of the terminal part 

 provided with a short spine at the end anteriorly. Caudal lamellae divided 

 into 2 rounded lobes, the anterior one trisetose, the posterior bisetose. Copu- 

 lative appendages of male with the terminal part rather small, lamelliform. 



Remarks. This genus is considered by G. W. Miiller to be a very 

 primitive type, and it is on that reason treated of at the very head of the 

 Cytheridce. I am not prepared to assent in this view. In my opinion it is 

 on the contrary considerably diverging from the usual Cytherid type, especially 





