OF THE COCCONEIDEiE. 



86\ 



ment. Hence the coipiisclcs on the npper, contiguous margin of each valve 

 appear as if crowned and enveloped (as it were, shielded) by the opposite setae 

 or membranes. 



Hercotheca mammillai'is (E.). — 

 Valves smooth, with the centre of the 

 base fringed romid (fortified) v.dth about 

 twenty simple, opposite setae, inserted 



on the margin itself, and extending be- 

 yond the mammillfe. EM. pi. 33. 18, 

 f. 7. Fossil. Bemiuda. (vn. 35.) 



FAMILY XIY.— COCCONEIDE^. 



Frustules elliptic, rarely bent, adnate by an inferior lateral surface, having 

 a median longitudinal line and central nodule. " The lateral surfaces prevail 

 so much that the central portion is reduced to a simple margin, and conse- 

 quently it is difficult to obtain a front view" (Meneg.). Campy lochscus and 

 Ehaphoneis, the only members of another family with which any of the 

 Cocconeideae are likely to be confounded, are distinguished by the absence of 

 a central nodule. Those species of jS"avicula which are eUiptic in the lateral 

 view somewhat resemble species of Cocconeis ; but they are never adnate, 

 and in them the central nodule is equally developed in both valves. 



Genus COCCONEIS (Ehr.). — Characters, those of the family. Fnistules 

 depressed or somewhat hemispherical ; the central nodule is wanting or 

 obscure in the inferior lateral surface, and sometimes there is a transverse 

 as well as a longitudinal line. " The general form of Cocconeis is that of a 

 disc of an ellipsoidal figure, with sm^faces more or less exactly parallel, plane, 

 or shghtly curved. . . . The characters by which the species of this most 

 elegant genus are distinguished one from another are still very slight " 

 (Meneg.). The frustules in this genus are frequently fiu^nished with an 

 additional membranous covering, which also forms a border to them, and has 

 been admitted into the specific definitions ; but we believe this envelope 

 generally, if not invariably, belongs to the immature state, and afterwards 

 disappears more or less completely ; and on this account we consider it an. 

 unsafe differential character. The descriptions apply to the lateral view, 

 unless otherwise stated. 



j smooth ; front view oblong, rectangular. 

 j KB. t. 4. £ 16. Coast of Normandy. 



1-1320". Nidulating in mucus. 

 I C. elongata (E.). — Small, smooth, 

 i oblono'-elliptic, plane. EM. pi. 5. 3. £ 26. 

 I America, Em-ope, Africa, China. Smaller 



than C. Placentula, but may be a variety 



of that species. 



C. Crux (E.). — Smooth, elliptic, thin, 



with a transverse linear umbilicus. KSA. 



p. 53. Western Asia. Diam. 1632". 

 C.dkq)hana(S.). — '^ Elliptical, scarcely 



silicious, diaphanous ; striss obscm-e. 



Length -0012" to -0018"." SBD. i. p. 22, 



pi. 30. £ 254. " /3, nodule dilated into a 



stam'os." Sidmouth, Jersey. 



C. Pediculus (E.). — Small, elliptic, 



somewhat angular, slightly curved ; disc 



with very fine, dotted longitudinal lines. 



SBD. i. p. 21, pi. 3. £ 31. Aquatic. 



Common. ^. salina (K.), narrower near 



the margin, furnished with very delicate 

 3k2 



* Disc smooth or icith longitudinal lines. 



Cocconeis longa (E.). — Very minute, 

 linear-oblong, with rounded ends, smooth, 

 except a median line and nodule. EM. 

 pi. 5. 1. £,25. Aquatic. Iceland. 



Q.pumila(K.). — Very minute, curved ; 

 lateral ^dew oblong-elliptic, smooth, 

 without lines or accessory border. KB. 

 pi. 5. 9. £ 2. Aquatic. Emope. Length 

 1-1560". Eabenhorst describes it as 

 destitute of median Hne and nodule. 



C. ivjgnKBci (K.). — Very minute, 

 smooth, eUiptic, girt by a crenidate ge- 

 latinous border. KB. t!^ 5. 6. £ 4. Baltic 

 Sea, on Ceramium. 1-2640". 



C. molesta (K.). — Minute, smooth, 

 elliptic-oblong, without an accessory 

 border, densely aggregated. KB. pi. 5. 

 7. £1,2. Marine. Venice. 1-1800" to 

 1-1680". 



C. nidulans (K.). — Elliptic-oblong, 



