82 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



cal, 007G ,um broad by about .057 nim long, composed of 8-10 cells in a row • 

 unilocular sporangia. 



Parasitic in the cryptostomata of Sargassum vulgar e. Summer. 



Wood's Holl, Mass. 



This species forms minute tufts on Sargassum, and is so small as easily to escape de- 

 tection. It is furthermore likely to bo mistaken for the hairs normally found at cer- 

 tain seasons in the cryptostomata. The description given above applies to the plant 

 found at Wood's Holl, which is smaller than the typical M. pulvinqta of Europe, which 

 grows in the cryptostomata of various Cystoseirce. In the European specimens ex- 

 amined the paraphyses were decidedly stouter, rarely being less than ,018 mm in breadth, 

 whereas with us they are seldom more than .010-12 mm broad. Our plant is through - 

 but smaller than the European, but, in proportion, the paraphyses are longer and 

 slenderer. It remains to be seen whether wo are correct in considering our form a 

 mere variety, or whether it should be kept distinct. Perhaps it may be the Phycophila 

 arabica of Kiitzing, Tab. Phyc, Vol. 8, PI. 1, Fig. 2, which grows on Cystoseira 

 myrica. The species is not uncommon in summer at Wood's Holl, and both forms of 

 sporangia occur together, the unilocular being much less abundant than the pluri- 

 locular. 



LEATHESIA, S. F. Gray. 



(Named in honor of Rev. G. B. Lcathes, a British naturalist.) 



Fronds olive-brown, gelatino-carnose, forming irregularly globose 

 masses, solid when young, but soon becoming hollow ; internal portion 

 composed of radiating, dichotomous filaments, formed of large, irregular, 

 colorless cells, the terminal ones bearing a series of short, simple, col- 

 ored filaments (paraphyses), which are densely packed together, consti- 

 tuting the cortical layer of the frond ; sporangia and hairs borne a.t the 

 base of the paraphyses ; plurilocular sporangia cylindrical, composed of 

 few cells in a siugle row; unilocular sporangia pyriform or ovoid. 



A small genus, comprising not more than half a dozen species, of which L. difformis 

 is common in the North Atlantic. Leathcsia Berkcleyi, Harv., now placed in the genus 

 PetrospongintiL, NVsg., although found not rarely in Europe and apparently tolerably 

 common on the coast of California, has not yet been detected in New England, but 

 may he expected. It forms rather leathery expansions on rocks at low-water mark. 



L. difformis, (Linn.) Arcsch. (Tremclla difformis, Linn., Syst. — 

 Ricularia tuherifor wis, Engl. Bot., PI. 1056. — Coryncphora marina, Ag., 

 Syst. — Leathesia tuberiformis, Gray, in Phyc. Brit., PI. 324, and Xer. Am. 

 Bor., Vol. I, PI. 10 c ; Thuret, in Ann. des Sciences, Ser. 3, Vol. XIV, PI. 

 2G, Figs. 5-12.) (PI. V, Fig. 1.) 



Fronds from half an inch to two inches in diameter, solitary or 

 aggregated, at first globose and solid, becoming irregularly lobed and 

 hollow; plurilocular sporangia produced early in the season, unilocular 

 sporangia in summer. 



