Structure of the Mouth in Sucking Crustacea, 305 



pair of maxillae are enclosed within the tube and have assumed 

 a shape adapted to action inside it. Whilst, therefore, the 

 rostrum in Isopoda contains mandibles and the first pair of 

 maxillae, Laphystius occupies the important stage in the deve- 

 lopment of the sucking-mouth in Crustacea where the rostrum 

 only contains mandibles. The oral formula for Laphystius 

 will consequently be the following. 



haphystius. 



Os haustellum. 



HausteUum adversum clypeo labroque, aversum labio malisque 

 exterioribus pedum maxillarium confectum, malas man- 

 dibulares serratorias involvens. 



Clypeus rotundate quadratus, fornicatus, pendulus. 



Labrum maximum, productum, conicum, acuminatum, fornica- 

 tum, pendulum. 



Mandibulce stipite producto, angusto, acuminato, depresso, 

 mobili, basi palpigero, malis binis. Mala exterior sub 

 labrum oblique inflexa, fixa, in orificiiim haustelli deor- 

 sum eminens, linearis, margine terminali arcuato, serrato. 

 Mala interior basi malte exterioris inserta, membranacea, 

 mobilis, minuta, linearis, apice trifida. Palpus clypeum 

 amplectens, triarticulatus, pervalidus, articulo terminali 

 inter antennas recepto, producto, conico, acuminato, in- 

 trorsum breviter setigero. 



Maxillae priores laminatae, malis binis, palpigerse. Mala exte- 

 rior falcata, apice spinis longioribus, validioribus, incurvis, 

 in series binas redactis armata. Mala interior brevis- 

 sima, conica, apice parce spinigera. Palpus perexiguus, 

 conicus, singulo constans articulo, conico, apice truncato, 

 breviter biseto. 



Maxilke posteriores laminatae, malis binis. Mala exterior 

 linearis, apice spinigera. Mala interior falcata, margine 

 interiore parce spinifero. 



Pedes maxillares cardinibus stipitibusque concretis, productis, 

 fornicatis, malis binis, palpigeri. Malce. exteriores amplae, 

 sinistra dextram obvolvente, fornicatse, apice late rotun- 

 datae, labro contigua. Malce interiores perminutae, conicae, 

 malis exterioribus contectae. Palpi minuti, conici, biar- 

 ticulati, malis exterioribus manifesto breviores. 



Labium amplum. Processus mandibulares angusti, acuminati, 

 retro directi. Lobi intermedii in lobos laterales confusi, 

 amplissimi, fornicati, dextro sinistrum obvolvente, apice 

 lingulati, mandibulas praeter apicem malae exterioris con- 

 tegentes. 



