384 C. E. Needier — Revision of the Families of 



by the growth of a septum in the middle of the dorsal valve, a 

 cistelliform stage is reached. From this point divergence begins, 

 and there is one series of transformations resulting^ in Macandrevia^ 

 and another terminating in Magellania^ the mature loops in both 

 groups being practically alike. Macandrevia and Dcdlina are mor- 

 phically equivalent to 3Iagellania, and Terehratalia is also in exact 

 parallelism with Terehratella. 



A more graphic presentation of the development and relations of 

 the genera is shown on Plate T, in which the stages of growth of 

 Magellania and Macandreviia are represented on two ontogenetic 

 lines. Outside are placed other species and genera, with their 

 known stages of grow^th so arranged that their equivalent stages 

 fall into parallel lines with those of Magellania and 3Iacandrevia.* 



The line begins in an early larval stage, Plate I, figure A, in 

 which there is a simple circlet of tentacles without a calcified loop, a 

 structure comparable in every respect with Gvninia^ figure Art. 



The next stage, Plate T, figure B, shows the growth of a septum 

 infiecting the line of tentacles, and producing an arrangement of 

 parts similar to Cistella^ although the loop is not calcified. The 

 completion of this structure results in Cistella, figure Bl, and speci- 

 mens having the characters presented by figures B, Bl, are referred 

 to the cistelliform stage. A fossil representative of this type is 

 Zellania, from the Jurassic, figure B«. 



3Iegathyris^ figure B2, offers nearly the same structure as Cistella, 

 but the growth of two lateral septa, or projections, has produced 

 two additional inflections in the loop. This completes the line of 

 development in the Megathyrinse. 



Next, considering the Dallininge in their ontogeny and mor- 

 phology, it is found that after passing through the gioyniform. and 

 cistelliform stages, Plate I, figures A, B, a form like Platidia is 

 reached, figure Cl, of which Platidia is the living adult representa- 

 tive, figure C4. The ^:)Za^zV?(/brm stage is shown in Macandreviia 

 cranium^ figures Cl, Dl ; Dallina septigera^ figure D2 ; D. flori- 

 dana^ figure C3; and 3Iuhlfeldtia sangidnea^ figures C2, D3. 



The growth of the secondary loop on the septum and the subse- 

 quent partial resorption produces a structure (I) like that in the 

 fossil genus IsmeJiia, and (2) one identical with that of adult Miihl- 

 feldtia (M. truncata and M. sanguinea). Plate I, figures E1-E5, 

 show the ismeniform stage of Macandrevia, Dallina, and Muhl- 



* The illustrations on Plate I are taken from Da\'idson,5' ^ Fischer and (Ehlert,* 

 Deslongchanips,'' and Friele," with original drawings by the writer. 



