{1158}The Phænocalpida are probably an artificial family, composed of three or four (or perhaps more) different groups, which have a quite different origin. The Litharachnida (genera 511-515) and the Haliphormida (genera 516-518) are probably derived from the Sethophormida by loss of the cephalis, the retrograde metamorphosis of which may be observed in all its different stages. The Halicalyptrida (genera 519-521) are perhaps independent of the other Phænocalpida, and may be Archicorida which have produced a corona of teeth around the mouth, without relation to lost radial ribs. The Phænoscenida (_Phænocalpis_, _Phænoscenium_) may be derived from the Euscenida (genera 504-507) by interpolation of interradial feet between the three primary ones, or directly from the #Plectoidea#. The Calpophænida, on the other hand (_Calpophæna_, _Archiphæna_), may have arisen from the Zygospyrida (_Petalospyris_, _Gorgospyris_) by loss of the sagittal ring and the longitudinal constriction. The phylogeny of the Phænocalpida is therefore a very complicated problem, as yet unsolved. _Synopsis of the Genera of Phænocalpida._ ------------------------------------------------------------------------- I. Subfamily Archiphormida. Basal mouth of the shell a simple wide opening. -------------------- Radial ribs enclosed in the wall of the shell, usually prolonged into free terminal feet. ------------------------------------------------------------------------- { Shell simple, with simple { network, 511. _Bathropyramis_. Shell slender, { pyramidal { Shell simple, with double (without horn). { network, 512. _Cinclopyramis_. { { Shell double, with an outer { mantle, 513. _Peripyramis_. Shell flatly } Radial ribs simple, 514. _Litharachnium_. campanulate or } discoidal (without } Radial ribs branched, 515. _Cladarachnium_. horn). } { Mouth smooth, constricted Shell ovate, { (no horn), 516. _Cystophormis_. urceolate or { campanulate. { Mouth, with { With horn, 517. _Haliphormis_. { a corona of { { feet. { No horn, 518. _Archiphormis_. ------------------------------------------------------------------------- No radial ribs in the wall of the shell. Mouth surrounded by a corona of free terminal feet. ------------------------------------------------------------------------- { With horn, 519. _Halicalyptra_. Shell simple without mantle. { { No horn, 520. _Carpocanistrum_.