274 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 3 



This species is one of the very common intertidal crustaceous coral- 

 lines in the northern Gulf. It has been taken on shore at several localities 

 besides that from which the type came. D. & R. 3162, cove north of Cabo 

 Arco, Guaymas; D. 416, 429, Pond Island; D. 465, San Esteban Island; 

 D. & R. 3383, intertidal pools, Punta San Pedro near Guaymas, Sonora, 

 December 22, 1939. The presence and horizontal arrangement of the 

 heterocysts seem to allow this species to be described under the genus 

 Porolithon. 



Considerable resemblance in form and structure is evident between 

 young examples of P. sonorensis and Lithothamnion mesomorphum var. 

 ornatum described from sterile material from the West Indies (Foslie & 

 Howe, 1906, p. 129). 



Genus DERMATOLITHON Foslie 



Dermatolithon veleroae sp. nov. 



Plate 62, Fig. 2 



Frondes tenues, prostratae usque ad assurgentes, in superficiebus conchae trans- 

 lucentis laxe afExae, coacervationes 1 cm. latas, valde imbricatae, exigue anasto- 

 mosantes formantes, crustis individuis 75-125 |x crassis; conceptaculis tetraspo- 

 rangiiferis hurailibus, tholiiformibus, circa 300 pidiam. extern., 100 M- altis, poro 

 singulo; tetrasporangiis 70-80 \i longis, columnam centralem paraphysium circum- 

 vallentibus; conceptaculis cystocarpiiferis forma magnitudineque tetrasporangi- 

 iferis similibus; conceptaculis spermatangiiferis 400 |x latis, 125 |J, altis, superficie 

 humili poro conico centrali ostioli excepto. 



Thallus thin, prostrate to ascending, growing loosely over surface of 

 a translucent shell and bits of attached Ulva as well as over crusts of its 

 own kind, forming patches about 1 cm. broad, all very weakly attached 

 and imbricated parts little or not at all anastomosed; crusts 75-125 jt* 

 thick^ composed of a hypothallic layer largely composed of vertically 

 elongated cells, and a perithallic superior portion of shorter, square to 

 oblong cells; all cells 6-11 /x, wide; tetrasporangial conceptacles low, dome 

 shaped, about 300 /* outside diam., 225 jit broad by 100 /x high inside; 

 tetrasporangia 70-80 [x long, borne around peripheiy of disk, the center 

 bearing a tuft of paraphj^ses ; cystocarpic conceptacles similar in size and 

 shape to tetrasporangial ones; antheridial conceptacles 400 ju, broad, 125 /* 

 high, outside, low except for a central ostiolar cone. 



Type: D. 550, on a shell picked up in middle littoral zone, Agua 

 Verde Bay, Feb. 12, 1940. Herb. AHF no. 26. 



This plant is known only from the single collection which fortunately 

 bears all reproductive organs. It is unique in its habit on shells, though the 

 specimen at hand shows the crusts growing up and over all objects at- 



