100 
GrevillEj on New Diatoms. 
PORPEIA. 
Porpeia quadriceps P Bail. — (Fig. 13.) 
Having obtained_, since the publication of my previous 
series, a most remarkable frustule of what I take to be a 
variety of this diatom^ I offer a figure of it in addition to my 
former illustrations. It will be perceived that Bailey^s draw- 
ing, as copied into Pritchard^s ' History of Infusoria ' (if, in- 
deed, it represents the same thing), indicates, when compared 
with our present diatom, a wide range of form. 
Heibergia, n. gen., Grev. 
Frustules compressed, quadrilateral, cellulate, with a punc- 
tate surface at the angles, where they probably cohere ; 
valves with one longitudinal and several transverse costse, 
the longitudinal one terminating towards each extremity in a 
blank space. 
This interesting genus, which I propose in honour of Dr. 
P. A. C. Heiberg, author of the valuable ' Conspectus Criti- 
cus Diatomacearum Danicarum,^ is nearly allied to BidduU 
phia, but differs in having a median costa terminating at 
each end in a definite blank space, and in the lateral valves 
not being constricted at their base. There appears also to be 
some affinity between this genus and Entogoniaj the broad 
borders of which, with their transverse costse, strongly re- 
semble the two sides of the valve of Heibergia, and the curious 
blank spaces near the ends of the valve in both genera seem 
quite analagous. 
Heibergia Barbadensis, n. sp., Grev. — (Pigs. 8 and 9.) 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq.; very rare. 
Frustules cellulate ; cellules hexagonal, conspicuous in the 
valves, minute in the connecting zone; the angles broadly 
and slightly mammillose, finely punctate. Yalves linear- 
oblong, longitudinally and transversely costate. The longi- 
tudinal or median costa terminating at each end in a subtii- 
angular blank space, which is separated from the punctate 
angles by a belt of cellules. Transverse costse 5 — 8, extend- 
ing from the median costa to the base of the valve, which is 
not constricted. All the costse are very slender and slightly 
flexuose. Length of valve •0055"'. 
