Probably the family Cyrtocalpida is an artificial group, comprising two or more different subfamilies of very different origin. The Cornutellida (_Cornutella_, _Cornutanna_) have probably been derived from the Sethocorida by loss of the cephalis, so that their conical shell represents a thorax alone. The Mitrocalpida on the other hand (genera 528-531) may be originally simple ovate shells (like _Gromia_ and _Lecythium_), arising independently from the Nassellida. The Archicapsida (_Halicapsa_, _Archicapsa_) are probably derived from the Zygospyrida (_Dictyospyris_, _Circospyris_) by loss of the sagittal ring and constriction. This is nearly certain, when the three or four typical cortinar pores appear in their basal plate. Some forms of _Halicapsa_ may be easily confounded with some forms of Prunoidea (_Lithapium_). Those Cyrtocalpida, which possess a central capsule with three or four lobes, are probably derived from Tripocyrtida by loss of the three feet, or from Sethocyrtida by loss of the cephalis, since the lobes indicate the original presence of cortinar pores and of a cephalis. Those Cyrtocalpida, however, in which a simple ovate shell encloses a simple central capsule without lobes, may be original "Monocyrtida eradiata," without relation to any radial ancestral forms. _Synopsis of the Genera of Cyrtocalpida._ ------------------------------------------------------------------------- I. Subfamily Archicorida. Basal mouth of the shell a simple wide opening. -------------------- Shell with simple lattice-work (not double or spongy). ------------------------------------------------------------------------- Shell conical, gradually { With horn, 526. _Cornutella_. dilated towards { the mouth. { No horn, 527. _Cornutanna_. Shell ovate or urceolate, { With horn, 528. _Archicorys_. with constricted { mouth. { No horn, 529. _Cyrtocalpis_ ------------------------------------------------------------------------- Shell not simply latticed. ------------------------------------------------------------------------- Shell ovate, double, with an external 530. _Mitrocalpis_. mantle, Shell ovate, with spongy irregular, lattice-work 531. _Spongocyrtis_. ------------------------------------------------------------------------- II. Subfamily Archicapsida. Mouth closed by a lattice plate. ------------------------------------------------------------------------- Shell with an apical horn, 532. _Halicapsa_. Shell without horn on the apex, 533. _Archicapsa_. {1180}Subfamily 1. ARCHICORIDA, Haeckel, 1881, Prodromus, p. 427. _Definition._--#Cyrtocalpida#, with the basal mouth of the shell open (vel Monocyrtida eradiata aperta). Genus 526. _Cornutella_,[143] Ehrenberg, 1838, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 128.