Naviculacea.] infosohial animalcules. 415 



scribed liereiu uudcr oue or othor of the sub-geuera. The sections 

 herein remain the same, viz. — 



a. — Form lanceolate, eighty species. 



b. — Eorm oblong or elliptic, twenty-nine species. 



c. — Form gibbous, sixteen species. 



d. — Form constricted or nodose, thirty species. 



e. — Form lunate, t"\;\ro species. 



/. — Form sigmoid, thirteen species. 



Sub-genus Pinnulaeia. — Umbilicus round ; surface transversely 

 striated. 



P. viridis. — Lorica transversely striated; straight, lanceolate, oblong; 

 obtuse and truncate at the ends ; striae fifteen in 1-1 200th. Common, 

 living and fossil. Figs. 133 and 134 represent living, and figs. 135 

 and 136 fossil forms. (P. 15, f. 15 and 31) ; the arrows in the two 

 first figures indicating the direction of the current produced. Length 

 1-1 150th to l-70th. In the interior, numerous changeable vesicles 

 are seen, connected together by means of an irritable gelatinous 

 matter, which is as clear as crystal, and from whose motion these 

 globules often appear to tremble. Ehrenberg has noticed moveable 

 dark spots near the extremity of some specimens, similar to what is 

 seen in Chsterium, &.c. The progress of longitudinal self-division 

 may often be observed beneath the siliceous lorica. The six openings 

 of the lorica are easily seen, tlu'ee being upon the upper sui'face and 

 three on the lower. The lorica near the central opening being 

 depressed, the aperture appears eccentric, in respect to the medial 

 line. Found at Hampstead, and fossil in Bohemia, Sweden, &c. 



P. mequalis. — Striated and unequally convex (see group 154.) ; of a 

 yellowish colour. In 1-lOOth of a line are ten or eleven striae. 

 This species forms the passage to the genus Eunotia. Found living, 

 at Tilbury Fort and elsewhere ; also fossil at San Fiore. Length 

 1 -430th to l-120th. The unequal sides in this species would render 

 it, in Kutzing's classification, a member of the genus Cymhella. 



P. macihnta. — Slender, elongated, attenuated towards the obtuse 

 rounded extremities; striag twenty-three in 1 -1200th; strong, 

 oblique, and converging to the centre. Fresh water and fossil. 

 Length 1- 140th. 



