4 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
lobus Eichwald 1860, Panderia Volborth 1863, Illaenurus Hall 1863, 
Illaenopsis Salter 1866, Ectillaenus, Hydrolaenus, Octillaenus Salter, 
1867, and Illaenoides Weller 1907. Certain other genera, such as 
Symphysurus and Nileus have often been placed with Illaenus, but 
they have more generally been recognized as belonging to the Asa- 
phidae. The fundamental difference between the Illaenidae and the 
Asaphidae is, of course, the presence in the former family of an 
epistoma, and its absence in the latter. The absence of the grooves 
on the pleura of the thorax in the Ilaenidae and their very general 
presence in the Asaphidae affords quite a safe criterion for judging 
of the dorsal surface. 
The genera enumerated above may be taken up in order. 
Cryptonymus Ejichwald, 1825. 
Observations geognostico-zoologicae per Ingriam marisque Baltici 
Provineias nec non de Trilobites. Casani, 1825, p. 44. 
In this paper, Eichwald, evidently not understanding Brongniart’s 
genus Asaphus, describes the new genus Cryptonymus, and under it, 
eight species. The first four are species of Asaphus and the last four 
are species of Illaenidae. Asaphus had been described in 1822, but 
Illaenus was not published till 1826, so that, if the four asaphids were 
eliminated, it would really leave an illaenid as the type of Cryptony- 
mus. The first of the illaenids described, Cryptonymus rosenbergi, is a 
Bumastus, the second, Cr. wahlenbergi, third, Cr. rudolphii, and the 
last, Cr. parkinsonit, are all species of Illaenus. To choose among 
these a type for Cryptonymus would be to upset one of two well- 
established names without any possible gain. Eichwald himself ac- 
cepted Illaenus as the name of these species, and in 1840 transferred 
his name Cryptonymus to Trilobites punctatus Wahlenberg, a pro- 
ceeding which he afterward stoutly defended (1855). If a new generic 
name is at any time necessary for any of the eight species described 
by Eichwald, Cryptonymus is still available, but till such a con- 
tingency arises, it seems best not to revive the name. 
Intaenus Dalman, 1826. 
Type, AsapHus crasstcaupA Wahlenberg. 
Om Palaeaderna eller de sa kallade Trilobiterna. Kgl. Vet. akad. 
Handl., 1826, p. 248. 
