M. Ussow's Zoolo(/ico-Embri/olo(/ical Investujatiuuft. 317 



ridges from the Leak to the ventral margin, separated by 

 slightly narrower deep coneave spaces ; near the beak (for 

 about half an inch) all the ribs set with strong blunt trans- 

 verse tubercles, about their own thickness apart (about five 

 in trwo lines), but on the adults the middle and lower ends of 

 the ribs are marked only with irregular lines of growth, like 

 the intervening hollows, except the seven or eight anterior 

 ones, on which the large blunt tuberculation is continued to 

 the ventral margin (about three in two lines). Length from 

 anterior to posterior end 2 inches 3 lines ; proportional width 

 from beak to opposite margin ^-''^o j depth of one valve tVo j 

 hinge-line -^Vo. 



This species is much larger, thicker, and stronger than the 

 living or the other two Tertiary species, and is readily distin- 

 guished by the tuberculation (except near the beak) being con- 

 fined ; the anterior ribs having, the middle and posterior ones 

 only slightly wrinkled by, lines of growth. The inner edge 

 is strongly toothed by the projecting ends of the channels 

 between the radiating ribs. Sometimes the two small most 

 posterior ridges bear tubercles. 



This species was collected by Mr. Howitt from the beds of 

 sandy marl at Jemmy's Point, near the entrance of the Gipps- 

 land lakes, containing Struthiolaria and other forms which I 

 have observed in the Pliocene Tertiaries of New Zealand, but 

 not of any other locality in Victoria. I have great pleasure 

 in naming so interesting a fossil after so excellent and zealous 

 a geologist as Mr. Howitt has proved himself in the Gipps- 

 land district. 



XLI. — Zoologico-Embryological Investigations. 

 By M. Ussow. 



[Concluded from p. 221.] 



Cephalopoda [conclusion). 



To render clearer all the processes described by me, I think 

 it will be useful to enumerate once more the principal facts of 

 the embryonal development of the above-mentioned Cephalo- 

 poda in their normal sequence. 



After the greater part of the protoplasm of the primitive 

 ovicell, or the formative vitellus which surrounds as with an 

 envelope the whole mass of the transparent fatty fluid (nutri- 

 tive vitellus) has been converted, in the manner already de- 

 scribed (see the process of segmentation), into a layer of flat 



