774 



SYSTEMATIC HISTORY OF THE INITSORIA. 



transverse costse, and moniliform, generally interrupted striae. Marine. 

 Plagiogramma is a well-marked genus, identical, we believe, -svith Heterom- 

 phala of Ehrenberg. We have adopted the present name, not^vithstanding 

 the prior claim of Ehrenberg's, because it is not only better defined, but the 

 latter was founded upon imperfect knowledge, when the lateral view, which 

 is so important, had not been observed. In the front view the terminal 

 puncta are very conspicuous and notch-like, so that the ends appear slightly 

 three-lobed, and the termination of the costoe and striae are conspicuous along 

 the lateral margins. The valves are always furnished with two central 

 transverse costae, and frequently with others. In addition to the costae there 

 are moniliform striae, — the former pervious, the latter, except in one species, 

 interrupted by a median line. We give Dr. Gre\iUe's arrangement of the 

 species, but must express a doubt whether the number of costae is not variable 

 in the same species. 



moniliform, 16 in -001". Grev /. c. p. 210, 

 pi. 10. f. 10. Jamaica and New Provi- 

 dence. Side view unknown. 



P. pi/ffniceum(Gve\.). — Minute; valves 

 narrow oblong ; costae four ; striae moni- 

 liform, interrupted, 21 in -001". Grev 

 /. c. p. 211, pi. 10. f 11. Distinguished 

 for its minute size, its shape, and the 

 small number of striae, although re- 

 latively closer. Grev. 



P. Grevillii (Ralfs). — Striae in front 

 view broad, moniliform, costate, 8 or 9 

 in -001"; costae four; connecting zone 

 Tsdth longitudinal rows of dots. = P. orna- 

 tum, Grev I c. p. 209, pi. 10. f. 9. CaU- 

 fomian guano. Side view unkno^vTi. 

 The striae are very peculiar, broad, at 

 first sight resembling costae. Grev. 



P. validum (Grev.). — Valve linear, 

 slightly dilated in the middle, roimded 

 at the ends ; costae four ; striae inter- 

 rupted, conspicuouslv moniliform, 12 in 

 •001". Grev I. c. p. 209, pi. 10. f. 8. Cah- 

 fomian guano. Front view unknown. 



P. ohesum (Grev.). — Minute valves, 

 broadly dilated at the middle and romided 

 at the ends ; costae four ; striae 11 in 

 •001". Grev I. c. p. 211, pi. 10. f. 12, 13. 

 New Providence. The inflated appear- 

 ance of the valves and the small number 

 of stride render this a well-marked spe- 

 cies, Grev. 



P. lymtiim (Grev.). — Valves con- 

 stricted at the middle, then dilated and 

 narrowly Ip-iform, linear, and rounded 

 at the extremities ; costae four; striae 18 



* Valves luith two centrical costce. 



Plagioghaimima Gregoriamim (Grev.). 

 — Front view mth slightly convex mar- 

 gins ; valves lanceolate oblong,^ obtuse ; 

 costae two; striae pervious, 18 in -001". 

 Grev. MJ. ^ii. p. 208, pi. 10. f. 1, 2. = 

 Denticula staurophora, Greg Diat. of 

 Clyde, p. 24, pi. 2. f 37. Scotland. _ 



P. Jamaicense .(GveY.). — Front view 

 with straight margins; striae continued 

 almost to the angles, 16 in -001" ; costae 

 two. Grev /. c. p. 208, pi. 10. f. 3. Ja- 

 maica. The striae can scarcely be termed 

 strictly moniliform, but rather monili- 

 form costae. Grev. 



P. ? tesseUatinn (Grev.). — Valves 

 broadly lanceolate, olituse; striae inter- 

 rupted, composed of large subquadrate 

 granules, 8 in -001"; costae tvv-o. Grev 

 I. c. p. 208, 1. 10. f 7. Californian guano. 



P. interruptum (Greg.). — Front \iew 

 with slightly convex margins ; costae 

 two ; striae obsolete ? = Denticula inter- 

 rupta, Greg Diat. of Clyde, p. 22, pi. 2. 

 f. 30. Scotland. Side view unknown. 



2 * Valves ivith two centrical costce and 

 one near each end. 



P. ornatum (Greg.).— Front ^dew with 

 convex margins, constricted beneath the 

 dilated ends ; costae four ; striae obsolete ? 

 = Denticula ornata, Gres- Diat. of Clyde, 

 p. 22, pi. 2. f. 32. Scotland. Side view 

 unknown. 



V. pulchelluni (Grev.). —Valve linear 

 oblong; costae four; striae robust, con- 

 spicuously moniliform, interrupted, 11 

 in '001". Grev /. c. p. 209, pi. 10. f. 4-6. 

 Californian guano ; Jamaica ; New Pro- 

 \ddence. 



P. incequale (Grev.). — Front view with 

 straight sides ; costae four, the terminal 

 ones in front view longer than the cen- 

 trical, and inflected at their apices ; striae 



in •OOl". Grev /. c. 

 New Providence. 



p. 211, pi. 10. 1 14. 



3* Valves with more than four costis. 



P. Californicum (Grev.). — Valves li- 

 near, with rounded ends ; costae more 

 than four; striae 18 in 001". Grev I c 

 p. 211, pi. 10. f. 15-17. Californian 

 guano. 



