4 54 PROCEEDINGS OF THE NATIONAL MUSEUM. 



tlio carina' of tlie i)roco(ling, wliilc in tlio otln^r Ibnr laniilios, ('yrtodos- 

 midit', HphaTiodosniidii', OyclodoHuiidH', Dasnionida^, the last segniont 

 is nmcli broador than tlio carina', and fornm a large rectangular plate 

 closing tlic posterior face of tiic strongly arched armor. 



Tills less perf'ecit armor and less convex body may be taken as reasons 

 for supposing that the Oniscodesmida' are less sjjecialized for the coil- 

 ing-up hal>it than the other fannlies, but as this adai)tation has evi- 

 dently arisen iiide[)endently in scvcial cases which tlius do not form a 

 phylogenetic series, there is less satislactioii in attempting to decide 

 which has i)roceeded furthest, even though the lines seem to converge. 



ANAI.Y'I'ICAI- KICY I'O THIC (ilONICItA OK ONlSCODlCSMlDiK. 



Por(^H )k)iiio oil (liHliiK't, roimdi^d (uIxtcIoh: (Jomia lAgnydcHmiis. 



Ton^H not laiHtxl al>ovt^ tlw Hiirfaco of I li«i HO^jiiitditH 



Boooiul Belmont Hoinowliat Hoinicirciiliir in laliTuI oiitliiio, without a postorior 

 aroiito border ; border of other HognxiiitN Hhoit; HiiiUH of 8cgm«uit 19 as broad iw its 

 oariiiiit: (ieniis DetodesmuH. 



Socrond MojjMU'Ht. iiicrtily obloiifj in lateral \ iiiw, with an areate border which 

 beroiiirs loiif'er on Huocecdin;; Hej;inentH; Minus of HOgnuuit 1!( lesH (ban half as wid(^ 

 an itH (^-irinic: (JennH OiitNctxIvti'miiii. 



Genus ON ISCODESM US Gervais and Goudot. 



OviarodfumiiK (iiCK\Ais and (Joi'Dot, Ann. Soc. ICiit. l''ranc(^ 1811, -d ser., II, ]>. 

 xxviii. 



The authors of (his genus described the first species as a Polydcsmns, 

 and at the end of the same paragraph erected the new genus for it. 



The body is less convex and more similar in shape to the Pterodes- 

 midje than in the species described by Peters under ()uisc(nh-nmu,s, but 

 which hav(^ been rccogni/.ed as independent genera, as ajjpears below. 



The other disiingiiishing feature of the present genus is the small 

 last segment, or rather the small i)art of the last segment, which can Im 

 s(u'ii from ab<>vt^ tlirough the small notch between the large carina' of 

 segment 1!>. 



ONISCODKSMUS ONISCINUS (Gcrvais and Goudot). 

 (I'iat.i \.\1X, li-is. 1((, 1''.) 



I'oliiileHtnus onisciniiH Okkvais and (loinor, Ann. Soc. Knt. Fiance, 1814, 2d 



tier., II, p. xxviii. 

 OniHoodeHViiiM oiiisoiniiB (Jicuvaih, Ann. Sci. Nat., ',k\ sor., I, j). (il, pi. v, fif;;H. 7, !>; 



Ai)tere8, 1847, IV, i). !K), id. xi.iv, (ig. 4. 



Ti/i>c. — A specimen supposiMl to be the type of this species is in the 

 JJritish Museum, and from this the two figures were traced. 



Loeality. — (>oIombia. 



From a ncsw spccMcs described below, (>. ovisrrniis dilVtMs more con- 

 si)icuously in the l)roa(ler notch of segment 11>, which in <). inicrKriis is 

 closed to a narrow slit, as may be seen from a comparison of the flgures. 



