8 Transactions of the 



berichte, 1844, p. 270. 0. subtiles sepimentis radiisque senis 

 areis radiantibus omnibus in subtilissimis lineis decussatis granu- 

 latis, hinc versicoloribus e fiisco rutilis radiis validus et umbilico 

 hexagono crystallino bene consi^icuis, margine tenui radiato, spinu- 

 lis areanum medio summo margine singulis ; diam. ^V of an inch, 

 ssepius minor ; Bermuda. 



Obs. Omnes Ompbalopelta, species Actinoptychum senarium 

 semulantur. 



Aulisctis seuljjtus or eselat%is; one of these names should be 

 cancelled, as the specific distinctions reUed upon by Dr. Greville are 

 of no value. The Iquique gathering yielding forms resembhng 

 both species ; the curious mastoid processes so conspicuous in this 

 genus in some specimens have their upper surfaces distinctly 

 granulate. 



The dredging from Pisagua contained some interesting forms, 

 the most abundant being Aulacodiscus margaritaceus ; some of the 

 valves are very fine (I have seen several nearly ^ of an inch in 

 diameter), the number of processes varying from 3 to 12. I have 

 occasionally found frustules the opposite valves of which differed in 

 the number of processes; in one instance one valve had four and the 

 other seven processes ; although as a rule the spaces between the 

 processes are equidistant, this is not invariably the case. I have one 

 valve with eight processes ; four of them occurring in pairs, each pair 

 being on opposite sides of the valve ; in another instance the valve has 

 three processes, two of which are close to each other, and the third 

 imperfectly developed on the opposite side of the valve ; Plate XXI. 

 (lower portion). Fig. 3. 



Auliscus racemosus rare, some five or six specimens have only 

 been found by myself, two about the size figured by Greville, and 

 the others nearly twice that size ; the marginal granules project dis- 

 tinctly fi-om the surface of the valve, the whole of which under an 

 8 objective is distinctly but delicately striate. 



A. Moronensis. — This form is rather more plentiful, but varies 

 much in size ; my largest specimen measures "0069, and the smallest 

 about -0030 in the larger diameter ; both of these had previously 

 only been found in fossil deposits, viz. that from Cambridge estate, 

 Barbadoes, and the Moron deposit, both of which I beheve belong 

 to the Miocene epoch : during this period the Diatomacete seem to 

 have made their first appearance. 



In a gathering from Callao, also made by Capt. Perry, A. 

 margaritaceus occurs sparingly, but a very fine Coscinodiscus, some 

 valves being as much as ^V of an inch in diameter, is common ; this 

 form is probably a robust state of C. i^erforatus. 



Several species of Navicula, some perhaps new, occur in the 

 gathering ; one with the outline of N. stranguJata, but with very 

 different markings, is, I believe, undescribed. The following are its 



