In leaving the Monhysterina, one ma.v note that prostomatal 

 teeth, if present, are anterior, small and subequal. Sometimes 

 a dorsal, anteriad pointing tooth is described in monhysterids. 

 Such a structure is present at the base of the stoma in Scap- 

 trella, it is non-selerotized, and is probably an esophageal de- 

 velopment through which the dorsal esophageal gland has its 

 orifiee. Heavily sclerotized dorsal teeth do not occur in this 

 group, a distinct contrast with the group to follow. 



CirROMADORiNA. Muscular esophageal tissue always sur- 

 rounds the protostom in members of this suborder (Fig. 61). 

 Forms with a rudimentary stoma are numerous but they arise 

 through collapse of the protostom rather than shortening. If 

 the protorhabdions are well sclerotized the cheilorhabdions 

 form odontia replacing the lips except in the Tripyloididae. 

 Onehial development is usually apparent, taking the form of a 

 large dorsal tooth opposed by smaller subventral ones. 



Chromadoroidea. Of this superfamily the Microlaimidae ap- 

 pear to be most primitive from the standpoint of stomatal char- 

 acters, including, as it does, forms with a subeylindrical pro- 

 tostom and protorhabdions terminated anteriorly by ouchia 

 (Etiimolaimiis revaliensis) . In this instance the dorsal onchium 

 is retrorse and the subventrals mere sclerotized oppositional 

 thickenings. In Statenia trichiira the same structure obtains 

 except that the subventral ouchia are also retrorse and but 

 slightly smaller than the dorsal. In MwroJaimiis dimorpluis 

 and Bolbdlainnis cabbi the dorsal onchia assume a mesostoma- 



tal position and are axially directed, the smaller subventral 

 onchia being slightly posterior and oppositional in character. 

 In all microlaimids tlie protorhabdions are moderately sclero- 

 tized and comi)letely surrounded by muscular esophageal tis- 

 sue; the base of tlie stomatal region is usually indicated by a 

 groove or tissue differentiation. Cheilorhabdions take the form 

 of 12 odontia replacing the lips in function but seldom pro- 

 truding beyond them. 



In the Chromadoridae examples of the same tendencies are 

 evident, Prochroiiiadora ncrlii)! corresponding to Stalinia and 

 Odonloncma gitido-schncideri to Bulbohiimtis. In addition the 

 stomatal region may not be set off posteriad (Chromadora, 

 Sj)iIop)toreUa paradoxa) ; the prostomatal dorsal onchium in 

 this case may be small or large, the protostom collapsed or 

 apparent. Cheilorhabdions take the form of 12 odontia as in 

 the Microlaimidae. 



In the Cyatholaimidae tliere are two chief stomatal types. 

 In the Cyatholaiminae the cheilorhabdions always take the form 

 of 12 conspicuous odontia which may pro.iect anteriorly be- 

 yond the labial region {Piimponcma mirabilc) ; the prostom 

 is wide, meso- and metastom narrow, with converging weakly 

 sclerotized mesorliabdions. A large dorsal axial onchium at 

 the junction of the pro- and mesostomata is usually present 

 and may be opposed by smaller subventral teeth (Acantlion- 

 cldis vivipanis). Choanolaims differ in that axial mesostonia- 

 tal teeth are inconspicuous or absent and the mesostom does 



Cephalic regions in the Chroinadorina. A-F — Microlaimidae. 

 G & U — Tripyloididae. H-K — Chromadoridae. L, N-S — Desmo- 

 doridae. M — Epsilonematidae. T — De.smoscolecidae. V-AA — 

 Cyatholaimidae. A — Aclirnmadora monohyntern ; H — Statenia tri- 

 chura; C — Aticrotninius diynorphus ; D — Ethmolainius revaUensis ; 

 K — HnlhntfiiiniiH rithhi : littlhotaimus rohhi (.section tllroii^h stoma- 

 tal rPKion): G — ltiitliiilainiu.s cnhhi. H — Chrnmndnrn sp. ; I — 

 Spilopliorflla /tnrtnloxa ; J — Prorhromndorn nrrlffii ; K — Odnulo- 

 Tlfma iiliida-Ni'hneideri; L — DeKtiindnra firaj(h'ii.\is ; M — Kfinilnnf- 

 iitnt'ul (s<'h('matic) : N — Crnconeiiiit iHitr/imilhitinri : O — Spirinn 

 piiraKJtifiTti ; I* — Mfla^hroinadnra anyxnidpti : Q — Mrtarh nitmt- 

 dorn nnyxii'uten (stomatal region) ; R — Metachromadora onyxoides 



(labial region) ; .S — Motwijnuthia hfxalata ; T — DpsmOHColex aitit'ii- 

 canus: V — Tripyhndea vittnaris: V — Acnnthonchvn rivipnrutt ; W 

 — Clieironrlnm bidbasa ; X — Halirhnniiolaimvs dolicharuti ; Y — 

 SynotH'hiplla inineatn; Z — Gnmmanfinia ferox; AA — Pomponeriia 

 mirahiU. (J — After Fililvtev. 1922, Art. Inst. .-Vgron. Slauropol., 

 V. 1 (IC). .1 & K— .\fter Filip.iev, 19:i0. Arch. Hydroliiril., v. 20. 

 Ij — After de Man, IHSH, Mem. Soc. Z.)c)l. France, v. 2. M — After 

 Steiner, 19:)0. Deutsche Sudpolar Expedition. N — After Steiner 

 & Hoeppli, 1926, Arch. Schiffs.-u, Tropenhyg., v. 30. O — After 

 Cohb, 1928, J. Wa.sh, Acad. Sc. W — After Filipjev, 1918, Trav. 

 Lab. Zool. Stat. Biol, Sebastopol, v, 2 (4). Remainder original. 



